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University of Groningen
Reactivity of rare earth metal organometallics bearing ancillary ligands derived the 1,4-Diazepan-6-amine frameworkGe, Shaozhong
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Reactivity of Rare Earth Metal Organometallics
Bearing Ancillary Ligands Derived from the
1,4-Diazepan-6-amine Framework
Shaozhong Ge
Reactivity of Rare Earth Metal Organometallics Bearing Ancillary Ligands Derived
from the 1,4-Diazepan-6-amine Framework
Shaozhong Ge
Cover picture: molecular structures of the trialkynyl yttrium complex (HL6)Y(C≡CPh)3
(front) and the dimeric dialkynyl yttrium complex [(L6)Y(C≡CPh)(μ-C≡CPh)]2 (back) (HL6:
N-(2-pyrrolidin-1-ylethyl)-1,4,6-trimethyl-1,4-diazepan-6-amine)
The research described in this thesis was carried out at the Stratingh Institute for Chemistry,
University of Groningen, the Netherlands and financially supported by the Chemical
Sciences division of the Netherlands Organization for Scientific Research (NWO-CW).
ISBN:
978-90-367-4060-9 (printed version)
978-90-367-4059-3 (electronic version)
RIJKSUNIVERSITEIT GRONINGEN
Reactivity of Rare Earth Metal Organometallics
Bearing Ancillary Ligands Derived from the
1,4-Diazepan-6-amine Framework
Proefschrift
ter verkrijging van het doctoraat in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit Groningen
op gezag van de Rector Magnificus, dr. F. Zwarts, in het openbaar te verdedigen op
maandag 26 oktober 2009 om 11:00 uur
door
Shaozhong Ge
geboren op 23 oktober 1980 te Anhui, P.R.China
Promotor: Prof. dr. B. Hessen
Beoordelingscommissie: Prof. dr. ir. H. J. Heeres
Prof. dr. ir. A. J. Minnaard
Prof. dr. J. Okuda
Contents
Chapter 1 Introduction ...........................................................................................................1
1.1. General Properties of Rare Earth Metals.........................................................................1
1.2 Organo Rare Earth Metal Chemistry................................................................................1
1.3 Ancillary Ligands for Cationic Rare Earth Organometallics............................................2
1.4 Neutral and Cationic Rare Earth Organometallics in Catalysis........................................7
1.5 Scope and Summary of the Thesis ...................................................................................7
1.6 References ........................................................................................................................9
Chapter 2 Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
..............................................................................................................................................13
2.1 Introduction....................................................................................................................13
2.2 Suitability Test of the 1,4,6-Trimethyl-1,4-diazepan-6-amine Group as Ligand Moiety
for Organo Rare Earth Metal Chemistry ..............................................................................14
2.3 1,4-Diazepan-6-amine-derived Ligands .........................................................................16
2.4 Concluding Remarks ......................................................................................................23
2.5 Experimental Section .....................................................................................................23
2.6 References:.....................................................................................................................33
Chapter 3 Rare Earth Metal Alkyl Complexes with fac-κ3 Nitrogen-based Neutral Ligand
Precursors.............................................................................................................................35
3.1 Introduction....................................................................................................................35
3.2 Synthesis of Neutral Organo Rare Earth Metal Complexes ...........................................36
3.3 Synthesis of Cationic Organo Rare Earth Metal Complexes with Neutral Ligand L1....43
3.4 Comparative catalysis study of intramolecular hydroamination cyclization of
aminoalkenes........................................................................................................................45
3.5 Concluding Remarks ......................................................................................................48
3.6 Experimental Section .....................................................................................................48
3.7 References ......................................................................................................................55
Chapter 4 Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido
Ligands.................................................................................................................................57
4.1 Introduction....................................................................................................................57
4.2 Reaction of One Equivalent of Ligand Precursor HL with Metal Alkyl Precursors ......58
4.3 Reaction of Two Equivalent of Ligand Precursor HL with Metal Alkyl Precursors ......64
4.4 Concluding Remarks ......................................................................................................73
4.5 Experimental Section .....................................................................................................73
4.6 References:.....................................................................................................................85
Chapter 5 Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived
from the Me3DAPA moiety ..................................................................................................87
5.1 Introduction....................................................................................................................87
5.2 Neutral Rare Earth Metal Dibenzyl Complexes .............................................................88
5.3 Generation of Cationic Species [(L)M(CH2R)]+ (R = Ph or SiMe3) ..............................97
5.4 Concluding Remarks ......................................................................................................98
5.5 Experimental Section .....................................................................................................98
5.6 References ....................................................................................................................112
Chapter 6 Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl
Complexes..........................................................................................................................113
6.1 Introduction..................................................................................................................113
6.2 Catalytic Dimerization of (Hetero)aromatic Terminal Alkynes by Neutral and Cationic
Rare Earth Metal Benzyl Complexes .................................................................................116
6.3. Isolation and Reactivity of Organo Rare Earth Metal Alkynyl Complexes.................121
6.4 Mechanistic Aspects of Catalytic Alkyne Dimerization by Neutral and Cationic Rare
Earth Metal Catalysts .........................................................................................................133
6.5. A One-pot Procedure for the Z-selective Catalytic Dimerization of Terminal Alkynes
with {HL6 + La[N(SiMe3)2]3}............................................................................................139
6.6 Concluding Remarks ....................................................................................................142
6.7 Experimental Section ...................................................................................................143
6.8 References ....................................................................................................................157
Chapter 7 Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from
the Me3DAPA moiety.........................................................................................................159
7.1 Introduction..................................................................................................................159
7.2 Organo Rare Earth Metal Complexes Supported by Tetradentate Dianionic Ligands
Derived form the Me3DAPA moiety ..................................................................................160
7.3 Catalytic Dimerization of Phenyacetylene ...................................................................167
7.4 Concluding Remarks ....................................................................................................167
7.5 Experimental Section ...................................................................................................167
7.6 References ....................................................................................................................171
Chapter 8 Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate
Ligands...............................................................................................................................175
8.1 Introduction..................................................................................................................175
8.2 Synthesis of a Sterically Demanding Guanidine ..........................................................176
8.3 Synthesis of Neutral Organo Rare Earth Metal Complexes with the Sterically
Demanding Guanidine Ligand HL19 ..................................................................................176
8.4 Generation of Cationic Species from Neutral Complexes 57-59 .................................183
8.5 Comparative Catalysis Study of Neutral and Cationic Complexes with Sterically
Demanding Amidinate and Guanidinate Ligands...............................................................184
8.6 Concluding Remarks ....................................................................................................190
8.7 Experimental Section ...................................................................................................191
8.8 References ....................................................................................................................198
Samenvatting......................................................................................................................201
Acknowledgement..............................................................................................................205
Introduction
1
Chapter 1 Introduction
1.1. General Properties of Rare Earth Metals
Rare earth metals include the group 3 metals (scandium and yttrium) and fifteen
lanthanide metals (from lanthanum to lutetium) in the periodic table.1 The most frequently
encountered oxidation state of these metals is +3, although four of them (Eu, Sm, Yb, and
Tm) can have divalent state and three (Ce, Pr, and Tb) a tetravalent state. For lanthanide
metals (with the general electronic configuration of [Xe]4fn5d16s2), the 4f valence orbitals
are strongly contracted on the metal center and do not significantly protrude beyond the filled
5d and 6s orbitals.2 As a result, the 4f electrons are assumed to be unavailable for bonding
and the metal ligand interactions are believed to be predominantly determined by
electrostatic and steric factors, rather than the metal-ligand orbital interactions. The ionic
radii of the rare earth metal ions M3+ (Sc, 0.75 Å; Y, 0.90 Å; La-Lu: 1.03-0.86 Å) are as a
whole larger than those of d-block transition metals (M3+: 0.62-0.76 Å; M4+: 0.60-0.79 Å)
with the exception of Sc3+.3
1.2 Organo Rare Earth Metal Chemistry
Organo rare earth metal complexes are molecular compounds of rare earth metals that
contain at least one metal-carbon bond. The first well-characterized organometallics of these
elements are the tris(cyclopentadienyl) complexes (Cp)3Ln, prepared in 1954 by Wilkinson
and Birmingham.4 In the mid-1970s, Tsutsui and Ely reported the sysnthesis of a series of
rare earth metal alkyl, allyl, aryl, and alkynyl complexes Cp2LnR (metallocenes) bearing two
cyclopentadienyl ligands.5 Since then, Cp-based ligands have dominated the organometallic
chemistry of rare earth metals for decades. During this course, a plethora of rare earth
organometallics bearing Cp-based ligands were synthesized, including metallocenes,
ansa-metallocnes (where two Cp ligands are linked with a bridging group), and subsequently
half-metallocenes (bearing mixed cyclopentadienyl-monodentate-anionic ligands).6 These
rare earth organometallics have been shown to be active catalysts, e.g. for olefin
polymerization, hydrogenation and hydrosilylation of alkenes, and intramolecular
hydroamination/cyclization of aminoolefins.6
Due to the Lewis acidity and the relatively large size of rare earth metal ions, syntheses of
organometallics derivatives of these metals are often accompanied by adduct formation with
Lewis bases or the formation of oligomeric species or so-called ‘ate’ complexes (essentially
adducts of anionic Lewis bases, the number of which then exceeds the valency of the metal
center).7 This leads to coordinative saturation of the metal centre, which makes these
complexes less reactive. This tendency to coordinative saturation can be countered by the use
Chapter 2
2
of sterically demanding ancillary ligands. For example, the sterically demanding
pentamethylcyclopentadienyl ligand (Cp*) was instrumental in gaining access to soluble,
monomeric and highly reactive rare earth metal metallocene complexes, and the sterically
demanding alkyl group CH(SiMe3)2 was essential in pioneering rare earth metal alkyl
chemistry.8
Although Cp-based ligands are suitable for the preparation of, and for reactivity studies on
well-defined monomeric rare earth organometallics, they do have their limitations. In
bis-cyclopentadienyl complexes, relatively little reactive space is left around the metal center,
and only one valence site is available for reactivity. The chemistry of mono-cyclopentadienyl
rare earth metal chemistry was slow to develop, requiring very sterically demanding
co-ligands and being susceptible to ligand redistribution (yielding stable metallocene
derivatives).6 Nevertheless, chemistry of rare earth metal compounds with two available
valence sites for reactivity is of interest, as it opens up the possibility to generate cationic rare
earth metal organometallics. Such cationic species were instrumental in early
transition-metal chemistry in accessing highly active single-site olefin polymerization
catalysts that led to a paradigm shift in organometallic catalysis.9 Thus great interest exists
for suitable monoanionic or neutral ancillary ligands that can support cationic rare earth
organometallic species. These cationic organometallic species have only emerged since the
late 1990’s,10 and their chemistry has been expanding at an increasing rate.
1.3 Ancillary Ligands for Cationic Rare Earth Organometallics
The chemistry of cationic rare earth organometallics has recently been the subject of
several reviews.6h, 11 Here we will not give a comprehensive survey, but describe
representative neutral and monoanionic non-cyclopentadienyl ligands that have been
instrumental in opening up the area of cationic organo rare earth metal chemistry. Substituted
cyclopentadienyl ligands [C5Me4R]- (R = Me10 and SiMe3)12 and donor functionalized
cyclopentadienyl ligands [C5Me4R]- (R = CH2CH2NMe213, C4H3O-2-SiMe2
14, and
CyPSiMe215) were reported to support cationic rare earth metal organometallics, but will not
been explicitly discussed here, as the focus of the work at hand lies on non-cyclopentadienyl
ancillary ligand systems.
1.3.1 Multidentate Neutral Ligands
Macrocyclic and tripodal ligands that contain nitrogen, oxygen, or sulfur donors (Scheme
1.1) have been used to support cationic rare earth alkyl complexes. In a seminal paper from
1997, Bercaw et al. showed that the scandium trimethyl complex (Me3TACN)ScMe3
(Me3TACN, I) reacted with B(C6F5)3 in THF to afford the contact ion pair
(Me3TACN)ScMe2(μ-Me)B(C6F5)3, which was an active catalyst for ethylene
polymerization.16 Subsequently, Mountford et al. reported that the scandium trialkyl
Introduction
3
complexes [(Me2pz)3CH]Sc(CH2SiMe3)3 ((Me2pz)3CH, III) and
(Me3TACN)Sc(CH2SiMe3)3, upon activation with B(C6F5)3, are also active catalysts in
ethylene polymerization.17 The reaction of (III)Sc(CH2SiMe3)3 with 1 equiv of
[Ph3C][B(C6F5)4] in the presence of 2 equiv of THF in CD2Cl2 solvent afforded
[(III)Sc(CH2SiMe3)2(THF)][B(C6F5)4], with a stable, THF-solvated cation. A sulfur
analogue of TACN, 1,4,7-trithiacyclononane (TTCN, IV) was also employed as neutral
tridentate ligand to supported organoscandium and yttrium ion pair
[(TTCN)M(CH2SiMe3)2(THF)x][B(C6F5)4] (M = Sc, x = 1; M = Y, x = 2), of which the
organoscandium compound was structurally characterized.18 Related to the fac-tridentate
neutral ligand III, a chiral trisoxazoline ligand (V) was used, by Gade et al. in 2005, to
stabilize the monocationic scandium dialkyl species [(V)Sc(CH2SiMe3)2][B(C6F5)4] and the
dicationic scandium monoalkyl [(V)Sc(CH2SiMe3)][B(C6F5)4]2;19 this dicationic monoalkyl
species is a highly active and isospecific catalyst for 1-hexene polymerization. Later, this
work was extended to other rare earth metals, such as Y, Dy, Ho, Er, Tm, and Lu.20
Scheme 1.1. Neutral Ligands for Cationic Rare Earth Organometallics
Another group of neutral ligands employed in this area are macrocyclic crown ethers. In
2002, Okuda et al. reported the use of crown ethers with different sizes as multidentate
neutral ligands for cationic organo rare earth chemistry and this work led to the first
structurally characterized rare earth metal alkyl cations, such as
[([12]-crown-4)LuR2(THF)]+, [([15]-crown-5)LuR2]+, and [([18]-crown-6)YR2]
+ (R =
CH2SiMe3).21 In 2003 they also reported the use of [12]-crown-4 ether (II) to generate a
range of cationic complexes for other rare earth metals, such as Sc, Y, Sm, Gd, Tb, Dy, Ho, Er,
Tm, Yb, and Lu.22 Later in 2005, the same research group reported the dicationic yttrium and
lutetium monoalkyl complexes, as well as tricationic alkyl-free complexes supported by
[12]-crown-4 ether.23
1.3.2 Mutlidentate Monoanionic ligands
1.3.2.1 Bidentate Nitrogen-based Monoanionic Ligands
In 2002, Hessen et al. reported the use of the sterically demanding amidinate
[PhC(N-2,6-iPr2C6H3)2]- (VI in Scheme 1.2, R = Ph) as monoanionic bidentate ligand for
Chapter 2
4
both neutral and cationic yttrium organometallics.24 Later it was shown that this ligand fits all
rare earth metals from smallest (scandium) to the largest (lanthanum) and a range of neutral
dialkyl and cationic monoalkyl rare earth metal complexes were isolated and studied as
catalyst for ethylene polymerization (living polymerization in some cases) and
hydroamination/cyclization of aminoalkenes.25 To test the versatility of this sterically
demanding amidinate, other aminidates, such as [C6F5C(N-2,6-iPr2C6H3)2]- and
[tBuC(N-2,6-iPr2C6H3)2]- (R = C6F5 or tBu, VI in Scheme 1.2), were developed and used to
support both neutral and cationic yttrium alkyl and lanthanum benzyl complexes.26 A related
family of bidentate monoanionic ligands, substituted 2-amidopyridines (VII, Scheme 1.2),
was reported to support neutral and cationic organoyttrium complexes.27 The in situ
generated ionic species [(VII)Y(CH2SiMe3)(THF)][B(C6F5)4] are active catalysts for
ethylene polymerization in the presence of TiBAO, producing aluminum-terminated
polyethylene with narrow molecular-weight distribution by reversible chain transfer between
organoyttrium cations and organoaluminum species.
Scheme 1.2. Bidentate Monoanionic Ligands for Catoinic Rare Earth Organometallics
Another type of monoanionic bidentate ligand that can be successfully employed in
cationic rare earth organometallics is the β-diketiminate family (VIII in Scheme 1.2, R = Me
or tBu) reported by Piers et al. A range of cationic scandium complexes bearing different
alkyl groups, such as methyl, benzyl and phenyldimethylsilylmethyl, with this ligand type
were prepared and studied as catalysts for ethylene polymerization and
hydroamination/cyclization of aminoalkenes.28 They also reported extensive studies on the
dynamics of the cation and anion in these cationic organoscandium complexes, and
mechanistic investigation of the arene exchange reaction of arene complexes of these
Introduction
5
organoscandium cations bearing β-diketiminate ligands.29 For cationic organoscandium
complexes bearing ligand VIII, the methyl groups of the iPr-substituents on the arene of the
ligand are susceptible to metalation by the Sc-alkyl bond;29b to overcome this problem, they
developed a very sterically demanding β-diketiminate ligand (IX in Scheme 1.2) that
avoids close CH…Sc interactions, and synthesized thermally robust cationic
organoscandium complexes with this bulky ligand.30 Although this type of ligand proved to
be very successful for cationic organscandium chemistry, synthesis of derivatives of other
rare earth metals proved not straightforward. Only very recently was extension of the
sterically demanding β-diketiminate ligand to cationic lanthanum benzyl and yttium alkyl
complexes reported by Hessen’s and Piers’s research group, respectively.26b,31 A closely
related anilido-imine ligand (X in Scheme 1.2) was used to support both neutral and
cationic yttrium complexes.32
1.3.2.2 Tridentate Monoanionic Ligands
Tridentate monoanionic ligands have seen only limited application in cationic rare earth
organometallics. In 2003, Gordon et al. reported the use of an anilido-pyridine-imine ligand
(XI in Scheme 1.3) in cationic organolutetium chemistry.33 Reaction of
(XI)Lu(CH2SiMe3)2 with B(C6F5)3 in the presence of THF in CD2Cl2 solvent afforded the
thermally stable ion pair [(XI)Lu(CH2SiMe2CH2SiMe3)(THF)][B(C6F5)3CH3]; this
unexpected transformation was explained by a concerted silyl methyl group abstraction by
B(C6F5)3 accompanied by alkyl migration. Another tridentate monoanionic ligand in this
area is the bis(pyrazoline)-amido ligand (XII in Scheme 1.3), developed by Mountford et
al..34 Reaction of (XII)Sc(CH2SiMe3)2 with [Ph3C][B(C6F5)4] in the presence of THF in
CD2Cl2 solvent on an NMR-tube scale afforded an ion pair
(XII)Sc(CH2SiMe3)(THF)][B(C6F5)4], which was shown to be an active catalyst for
ethylene polymerization. In 2007, Hou et al. reported the use of a monoanionic PNP pincer
ligand (XIII) to support cationic rare earth metal organometallics.35 Reaction of neutral
dialkyl complexes (XIII)M(CH2SiMe3)2(THF)x (M = Sc, x =0; M = Y or Lu, x = 1) with
[PhNMe2H][B(C6F5)4] in THF solvent afforded the thermally stable ion pairs
[(XIII)M(CH2SiMe3)(THF)x][B(C6F5)4] (x = 2); the in situ generated cationic species in
C6H5Cl catalyze the living cis-1,4-polymerization and copolymerization of isoprene and
butadiene.
Scheme 1.3. Tridentate Monoanionic Ligands for Cationic Rare Earth Organometallics.
Chapter 2
6
1.3.2.3 Tetradentate Monoanionic Ligands
Thus far, tetradentate monoanionic ligands for cationic organo rare earth metal chemistry
are limited to functionalized 1,4,7-triazacyclononane ligands with a pendant anionic
functionality (XIV: B = CH2CH2 or SiMe2 and R = tBu, secBu, and nBu; XV: B = CH2CH2
or SiMe2, in Scheme 1.4) and related non-cyclic triamino-amido ligands (XVI: B =
CH2CH2 or SiMe2, in Scheme 1.4), developed by Hessen’s research group. The cationic
species [(XIV)M(CH2SiMe3)][B(C6F5)4] (M = Sc, Y, Nd, and La) were prepared on
NMR-tube scale by reaction of the corresponding dialkyl complex (XIV)M(CH2SiMe3)2
with 1 equiv of [PhNMe2H][B(C6F5)4] in the weakly coordinating polar solvent C6D5Br;
these cationic species are sufficiently stable to allow for characterization by 1H NMR
spectroscopy at ambient temperature and are active catalysts for ethylene polymerization.36
In contrast, reaction of (XV)M(CH2SiMe3)2 (M = Y and La) with 1 equiv of
[PhNMe2H][B(C6F5)4] in C6D5Br instantaneously liberates two equiv of TMS and 1 equiv
of propene (as seen by 1H NMR spectroscopy) and no well-defined organometallic
products were observed; this might be due to thermal instability of the initially formed
cationic species. Such decomposition can be prevented when these reactions are performed
in THF.37 The yttrium complexes [(XV)Y(CH2SiMe3)(THF)][BPh4] were isolated (stable
for days at ambient temperature) and structurally characterized, whereas the lanthanum
cations [(XV)La(CH2SiMe3)(THF-d8)x] could only be generated in situ and gradually
decompose. The thermal decomposition of these species was studied by ES-MS
(electrospray mass spectroscopy) and involves initial cyclometalation of the iPr group in
the ligand, followed by propene extrusion via -N elimination. Additionally, the cationic
yttrium complex [(XVI)Y(CH2SiMe3)(THF-d8)x]+ was generated to compare the reactivity
with its amide-functionalized Me2TACN analogue.38 Mountford et al. also reported a
functionalized 1,4,7-triazacyclononane ligand XVII (Scheme 1.4) with a pendant
phenoxide in 2001 and a neutral scandium dialkyl complex of this ligand
(XVII)Sc(CH2SiMe3)2 was prepared;39 however, subsequent attempts to generate the
cationic species from this neutral dialkyl complex resulted in ill-defined mixtures.17
Scheme 1.4. Tetradentate Monoanionic Ligands for Cationic Rare Earth Organometallics
Introduction
7
1.4 Neutral and Cationic Rare Earth Organometallics in Catalysis
Neutral rare earth organometallics have been extensively investigated as catalysts for
olefin polymerization and it was shown that especially neutral metallocene alkyl and
hydrido complexes are highly active towards ethylene.40 They also found applications in
organic synthesis;41 most of such catalytic applications involve alkyne and alkene
transformation, such as cyclization,42 hydrogenation,43 hydroamination,44 hydrosilylation,45
hydrophosphination,46 hydroboration,47 and oligomerization.48 Some of these reactions
were shown to proceed with high regio- and stereoselectivity and a high tolerance towards
functionalized substrates. Particularly, organo rare earth complexes can effectively catalyze
the intramolecular hydroamination/cyclization of aminoalkenes, aminoalkynes,
aminoallenes, and tandem bicyclization of aminodienes, aminodiynes, and aminoenynes,
with high regio-, diastereo-, or enantioselectivity.49
Cationic rare earth organometallics are mainly studied for homo- and copolymerization
of nonpolar olefins, such as ethylene polymerization,17,24,25a,28c,d,36a,c 1-hexene
polymerization,18a,19,20 styrene polymerization,12b,18a 1,3-diene polymerization,12h,j,15
isobutylene polymerization,50 and ethylene/styrene copolymerization.12b,c Efforts to apply
these cationic organometallics to organic synthesis have only recently begun; Piers et al.
reported a cationic organoscandium catalyst bearing a β-diketiminate ligand for
intramolecular hydroamination/cyclization of aminoalkenes with increased activity
compared with the neutral catalyst.28e Later in 2005, Hessen et al. showed that, for
intramolecular hydroamination/cyclization, the relative activity of neutral vs cationic
catalysts is highly dependent on the nature of the ancillary ligand of the catalyst.25b Another
reaction catalyzed by the cationic rare earth alkyl complex is Z-selective linear
dimerization of phenylacetylene,36c with a significant increase in tof (turnover frequency)
compared with neutral half-metallocene catalysts of rare earth metals.
1.5 Scope and Summary of the Thesis
When the work described in this thesis started, the cationic organometallic chemistry of
rare earth metals was still in its infancy compared to that of transition metals. The aim of
this thesis was to explore the reactivity and catalytic properties of well-defined neutral and
cationic rare earth organometallics with an ancillary ligand system that allows for
systematic variations. For this purpose, we have developed a series of neutral and
monoanionic chelating ancillary ligands based on the 1,4,6-trimethyl-1,4-diazepan-6-amine
(Me3DAPA) moiety and prepared a range of well-defined neutral and cationic rare earth
metal alkyl and benzyl complexes supported by these ligands. These organometallic
complexes were studied for catalytic ethylene polymerization, intramolecular
hydroamination/cyclization, linear dimerization of terminal alkynes, and hydrosilylation of
terminal alkenes. As to the rare earth metals studied, we have limited ourselves to scandium,
Chapter 2
8
yttrium, and lanthanum for two main reasons: (1) these metals are diamagnetic and the
complexes of these metals and their reactivity can be conveniently studied by NMR
spectroscopy; furthermore, yttrium is NMR active (89Y, natural abundance of 100% and I =
1/2) and Y-C and Y-H couplings provide valuable structural information for the compounds
in solution. (2) The ionic radii of these three metals (for 6-coordinated ions: Sc3+, 0.75 Å;
Y3+, 0.90 Å; La3+, 1.03 Å) span the full size range of the rare earth series, thus the
chemistry observed for these metals can be projected on other metals of the series in the
appropriate size range.
In Chapter 2, it is first shown that the 1,4,6-trimethyl-1,4-diazepan-6-amine group can act
as a suitable ancillary ligand moiety for neutral and cationic rare earth organometallics.
Subsequently, the synthesis of a series of ligands (neutral and monoanionic tridentate ligands,
and neutral, monoanionic, and dianionic tetradentate ligands) based on this ligand
framework is described.
In Chapter 3, the synthesis and characterization is described of neutral and cationic
trimethylsilylmethyl (for Sc and Y) and benzyl (for Sc and La) complexes bearing a neutral
tridentate 1,4,7-trimethyl-1,4-diazepan-6-amine ligand. A comparative study of catalytic
intramolecular hydroamination/cyclization of aminoolefins with the synthesized complexes
as catalysts is carried out to probe the dependence of the relative catalyst performances of
neutral and cationic species on the metal size for the neutral N3 ancillary ligand system.
In Chapter 4, we describe the application of monoanionic 1,4-diazepan-6-amido ligands to
organoscandium and -yttrium chemistry. This study reveals that there are accessible
pathways for ligand decomposition by metalation of the methyl group on the amido nitrogen
in the ligand N,1,4,6-tetramethyl-1,4-diazepan-6-amine (Me4DAPA, L3) and by
ring-opening reactions of the 1,4-diazepane ring, induced by metalation of the ethylene
bridge between two of the ligand N atoms.
In Chapter 5, the synthesis and characterization of neutral dibenzyl and cationic
monobenzyl complexes of scandium, yttrium, and lanthanum bearing monoanionic
tetradentate ligands is described and this allows comparative studies on their catalytic
performances for catalytic Z-selective linear dimerization of terminal alkynes, which is
described in Chapter 6. The effects of metal ion size, ancillary ligand, and use of neutral vs
cationic catalyst on catalyst performances have been investigated. Stoichiometric reactions
established the identity of the reaction intermediates observed during the catalytic substrate
conversion. Based on the reactivity of isolated products from stoichiometric reactions and
kinetic studies on the catalysis, a new reaction scheme has been proposed to explain the
observed Z-selectivity for the linear dimerization reaction of terminal alkynes.
In Chapter 7, the application of tetradentate dianionic ligands derived from
1,4-diazepan-6-amine to the synthesis of neutral rare earth organometallics is described. The
synthesized neutral organometallics were employed as catalysts for the dimerization of
Introduction
9
phenylacetylene and it is shown that the ancillary ligand and metal ion size have visible
influences on the rate of conversion.
In Chapter 8, we describe the use of another type of ligand, the sterically demanding
guanidinate [Me2NC(NAr)2]- (Ar = 2,6-iPr2C6H3), for synthesis of a range of neutral and
cationic scandium, yttrium, and lanthanum alkyl complexes. A comparative study of their
performances in the catalytic hydroamination/cyclization reaction of aminoolefins and the
hydrosilylation reaction of terminal alkenes has been performed. Combined with a catalysis
study of the yttrium dialkyl complexes bearing the sterically demanding amidinate
[RNC(NAr)2]- (VI in Scheme 1.2, R = Ph, Me-p-Ph, and C6F5; Ar = 2,6-iPr2C6H3), we show
how the steric and electronic properties of the ancillary ligands affect the catalytic
performance of this family of catalysts.
1.6 References
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Chapter 2
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Chapter 2
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Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
13
Chapter 2 Synthesis of Ancillary Ligands Based on the
1,4-Diazepan-6-amine Framework
2.1 Introduction
In contrast to their transition-metal analogues, which have long been known as active
catalysts for olefin polymerisation, cationic rare earth metal organometallic compounds have
only recently become available.1 The use of nitrogen-based facial tridentate ligand moieties,
such as 1,4,7-triazacyclononane, tris(pyrazolyl)methane and tris(oxazolinyl)ethane, has
played an important role in opening up this chemistry.2 However, the stepwise modification
and systematic extension of these moieties are synthetically quite elaborate. As little is
known as yet about ligand effects on the reactive and catalytic properties of cationic rare
earth metal organometallics, it would be of great interest to find a ligand framework that
allows for convenient systematic variations. Very recently, the use of the
1,4-diazepan-6-amine group as a facially coordinating moiety in biomimetic complexes was
described.3 A slightly modified version of this group, 1,4,6-trimethyl-1,4-diazepan-6-amine
(Me3DAPA), is readily obtained by reaction of N,N’-dimethylethane-1,2-diamine with
nitroethane and formaldehyde (as shown in Scheme 2.1), followed by reduction of the nitro
group.4
In this chapter, we show that the Me3DAPA group can be used as ligand framework for
both neutral and cationic scandium and yttrium alkyl chemistry. It also provides a versatile
basis for a range of neutral and anionic tri-, tetra-, and hexadentate ancillary ligands.
Scheme 2.1. Synthesis of 1,4,6-Trimethyl-1,4-diazepan-6-amine (Me3DAPA).4
2.2 Suitability Test of the 1,4,6-Trimethyl-1,4-diazepan-6-amine Group
as Ligand Moiety for Organo Rare Earth Metal Chemistry
To test the suitability of the Me3DAPA group as an ancillary ligand moiety for organo rare
earth metal chemistry, the known permethylated 6-methyl-1,4-diazepan-6-amine (L) was
reacted with the group 3 metal trialkyls M(CH2SiMe3)3(THF)2 (M = Sc, Y).5 This afforded
Chapter 2
14
the complexes (L)M(CH2SiMe3)3 (M = Sc, 1; Y, 2; Scheme 2.2) in high isolated yields (1:
94%; 2: 95%). Solution NMR spectroscopy of these compounds (C7D8) showed that the
three alkyl groups on the metal centre are equivalent down to -50 oC. The M-CH2 resonances
(in C6D6) for 1 are found at δ -0.14 ppm (1H) and δ 40.0 ppm (13C), for 2 at δ -0.56 (d, 1JYH =
2.9 Hz) and δ 36.9 ppm (JYC = 35 Hz) respectively.
Scheme 2.2. Synthesis of Neutral and Cationic Me3DAPA Scandium and Yttrium Alkyl
Complexes.
Figure 2.1. Molecular structure of one of independent molecules of 1. All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability
level. Selected bond distances (Å) and angles (°): Sc(1)-N(11) = 2.540(3), Sc(1)-N(12) = 2.465(3), Sc(1)-N(3) = 2.521(3), Sc(1)-C(111) = 2.267(3), Sc(1)-C(115) = 2.256(4),
Sc(1)-C(119) = 2.309(4); N(12)-Sc(1)-N(13) = 66.45(8), N(11)-Sc(1)-C(119) 159.47(11), N(12)-Sc(1)-C(111) = 163.19(11), N(13)-Sc(1)-C(115) = 153.24(11).
A crystal structure determination of 1 was performed, and its molecular structure is shown
in Figure 2.1, together with selected bond lengths and angles. The crystal contains two
independent molecules in the asymmetric unit, which do not differ significantly; only one is
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
15
explicitly discussed here. The three nitrogen atoms of L are bound to the scandium centre in
a fac-arrangement and the geometry at Sc is approximately octahedral. The average Sc-N
bond length of 2.497 Å in 1 is slightly longer than that reported for the triazacyclononane
complex Sc(Me3[9]aneN3)(CH2SiMe3)32c (average 2.463 Å), while the average Sc-CH2
distances are very similar. There is no notable asymmetry in the bonding of the three amine
donors in 1: the Sc-N distance for the NMe2-group is intermediate between the other two
Sc-N distances in the complex. The smallest N-Sc-N angle involves the amine nitrogen
atoms linked by the (CH2)2-bridge: N(12)-Sc(1)-N(13) = 66.45(8)o.
The neutral trialkyl complexes can be converted in THF solvent to the dialkyl cations
[(L)M(CH2SiMe3)2(THF)]+ (M = Sc, 3; Y, 4) by reaction with [PhNMe2H][BAr4] (Ar = Ph,
C6F5). This was seen by NMR spectroscopy when performing these reactions in THF-d8, and
the BPh4-salt of the Sc cation 3 was isolated in 75% yield from THF/cyclohexane. The 13C
NMR resonances of the M-CH2 groups in cationic species relative to those in their
corresponding neutral precursors show the typical downfield shift and (for Y) increase in 1JYC associated with conversion to the cationic species (for 2: δ 42.3 ppm, 1JYC = 41 Hz).6
Ethylene polymerization experiments with 1 and 2 activated by [PhNMe2H][B(C6F5)4]
were performed in toluene, and the results are listed in Table 2.1. For both metals active
polymerization catalysts are obtained. This shows that the 6-methyl-1,4-diazepan-6-amine
group is suitable as ancillary ligand moiety for cationic rare earth metal alkyl catalysts.
Remarkably, the activity of the Sc system increases substantially when the temperature is
increased from 50 oC to 70 oC, but this is accompanied by a strong broadening of the polymer
molecular weight distribution. This might be due to the transformation of the initially formed
cation into another species that is also active, and of which the nature is presently unclear.
Table 2.1. Catalytic ethylene polymerization with [(L)M(CH2SiMe3)3] (M = Sc, 1; Y, 2)
activated with [PhMe2NH][B(C6F5)4].a
Catalyst
precursor
T/°C PE yield/g Productivity/102 kg(PE)
mol(M)-1 h-1 bar-1
10-5Mw Mw/Mn
1 50 4.43 5.32 9.32 3.0
1 70 9.66 11.60 2.35 9.4
2 50 3.24 3.89 4.95 3.1
2 70 4.57 5.48 1.43 2.6
a Conditions: 1 L steel autoclave (stirring rate 600 rpm), 250 mL toluene, 10 μmol catalyst
precursor, 10 μmol [PhMe2NH][B(C6F5)4], 5 bar ethylene, 10 min run time.
2.3 1,4-Diazepan-6-amine-derived Ligands
As described above, the Me3DAPA moiety is a suitable ligand framework for neutral and
cationic rare earth organometallic chemistry. Subsequently, we developed a series of neutral
Chapter 2
16
and monoanionic chelating ligands, as shown in Scheme 2.3, by functionalizing this moiety.
These ligand derivatives were made via the conventional C-N bond formation reactions (e.g.
nucleophilic substitution reactions between primary amine and alkylhalide or imidoylhalide,
the acid-catalyzed condensation reaction between primary amine and aldehyde followed by
reduction of the imino group, and acetamide formation reactions followed by reduction of
the carbonyl functionality) or Si-N bond formation reactions (nucleophilic substitution
reactions between amines and chlorosilanes in the presence of base or metathesis reactions
between metal amides and chlorosilanes). In the following part of this chapter, the synthesis
of each ligand will be explicitly discussed.
Scheme 2.3. Overview of Ligand Types Derived from the Me3DAPA Moiety (B is a
bridging moiety).
2.3.1 Synthesis of Neutral fac-Tridentate Ligands L1 and L2
Two neutral tridentate ligands 1,4,6-trimethyl-6-pyrrolidin-1-yl-1,4-diazepane (L1) and
1,4,6-trimethyl-N-phenylmethylene-1,4-diazepan-6-amine (L2) were developed. Ligand L1
can be conveniently prepared by reaction of Me3DAPA with 1,4-dibromobutane in the
presence of K2CO3 in ethanol (Scheme 2.4), a general procedure described for pyrrolidine
synthesis.7 It was isolated as a colorless liquid with a yield of 57% after distillation. Ligand
L2 was synthesized by the acid-catalyzed condensation of Me3DAPA with benzaldehyde
(Scheme 2.4). It was isolated as a slightly yellow liquid with a yield of 74%. These two
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
17
ligands were characterized by 1H and 13C NMR spectroscopy and elemental analysis. The
NMR resonances (in C6D6) of the N=CH group in L2 is found at δ 8.57 ppm (1H) and δ
156.6 ppm (13C).
Scheme 2.4. Synthesis of Ligands L1 and L2.
2.3.2 Synthesis of Tridentate Ligands HL3 and HL4 with an Active Hydrogen on the 6-Amine Nitrogen of the Me3DAPA Moiety
Two such ligands, N,1,4,6-tetramethyl-1,4-diazepan-6-amine (Me4DAPA, HL3) and
N-dimethylphenylsilyl-1,4,6-trimethyl-1,4-diazepan-6-amine (HL4), were developed. HL3
was prepared by reaction of Me3DAPA with ethyl formate under refluxing conditions,
followed by reduction with LiAlH4 in refluxing diethyl ether. It was isolated as a colorless
liquid in 74% yield after hydrolysis and distillation (Scheme 2.5). HL4 was prepared by the
lithiation of 1,4,6-trimethyl-1,4-diazepan-6-amine with n-BuLi, followed by addition of
Me2PhSiCl (Scheme 2.5). It was isolated as a colorless liquid (95% purity by 1H NMR) in
74% yield after distillation. These two ligands were characterized by NMR (1H and 13C)
spectroscopy and elemental analysis. The 1H NMR resonance of NH of HL3 was not
observed, while that of HL4 in C6D6 is present at δ 1.97 ppm.
Scheme 2.5. Synthesis of Ligands HL3 and HL4.
Chapter 2
18
2.3.3 Synthesis of Monoanionic Tetradentate Ligands
2.3.3.1 N3O-Ligand with an Active Hydrogen on the Oxygen Atom
The salicylaldiminato framework has a long history as an ancillary ligand in coordination
and organometallic chemistry. Recently, its bulky derivatives have been employed in
preparing scandium and yttrium alkyl complexes.8 Nevertheless, the resulting complexes are
thermally labile and decompose via H-abstraction from the ligand or alkylation of the imino
functionality in the ligand backbone. In order to improve the thermal stability of this type of
rare earth organometallics, we intended to functionalize the salicylaldiminato moiety with
additional nitrogen donors, and designed the tetradentate ligand precursor HL5, with an
active proton on the oxygen atom (Scheme 2.6). This ligand was synthesized by the
acid-catalyzed condensation reaction of salicylaldehyde with Me3DAPA in ethanol. It was
obtained (isolated yield: 65%) as a yellow liquid after Kugelrohr distillation. This compound
was characterized by 1H and 13C NMR spectroscopy and elemental analysis. The NMR
resonances (in C6D6) of the N=CH group in HL5 are present at δ 8.48 ppm (1H) and δ 162.0
ppm (13C).
Scheme 2.6. Synthesis of Ligand HL5.
2.3.3.2 N4-Ligands with an Active Hydrogen on the 6-Amine Nitrogen of the Me3DAPA Moiety
We developed three ancillary ligands of this type: HL5, HL7, and HL8 as shown in Scheme
2.7. Ligand HL6 was prepared in three steps from Me3DAPA (Scheme 2.7) and this
procedure was employed earlier in our group to functionalize the 1,4,7-triazacyclononane
moiety to form the Me2TACN-amide ligand.6a Reaction of chloroacetyl chloride with
Me3DAPA under basic conditions afforded A, reaction of A with pyrrolidine and a catalytic
amount of NaI in acetonitrile solvent yielded B, and the reduction of the carbonyl
functionality in B by LiAlH4 in di-n-butyl ether followed by aqueous workup afforded HL5
as a colorless liquid in 81% yield after Kugelrohr distillation. Ligand HL7 is conveniently
prepared by condensation of 2-pyrrolidin-1-ylbenzaldehyde with Me3DAPA, followed by
reduction of the imino functionality with NaBH4 in methanol (Scheme 2.7). It was obtained
(isolated yield: 87%) as a colorless liquid after distillation. Ligand HL8 with the
dimethylsilyl bridge is most conveniently prepared by the lithiation of Me3DAPA with
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
19
n-BuLi, followed by reaction with pyrrolidin-1-yldimethylsilyl chloride (Scheme 2.7). It was
isolated in 76% yield as a colorless liquid after distillation. Ligand HL8 is susceptible to
hydrolysis and was stored under a dry nitrogen atmosphere. These three compounds were
characterized by 1H and 13C NMR spectroscopy and elemental analysis. The 1H resonances
(in C6D6) of NH in HL6 and HL7 were not detected and that in HL8 was found at δ 1.76 ppm.
Scheme 2.7. Synthesis of monoanionic tetradentate ligands HL6, HL7, and HL8.
2.3.3.2 N4-Ligands with an Amidine Backbone (Hybrid Ligands of the Benzamidinate and the 1,4-Diazepan-6-amido Ligand Moieties)
The N,N’-bis(trimethylsilyl or aryl) benzamidinate units have been extensively used in the
past as ancillary ligands in the field of main group, transition, and rare earth metal
chemistry.9 Recently, functionalized amidinate ligands such as bis(amidinate) ligands linked
by the dimethylsilyl or (CH2)3 bridge and amino-amidinate ligands, have been successfully
synthesized and used as ancillary ligands for orgnaometallic and coordinative rare earth
metal chemistry.10 Here we functionalized the 1,4-diazepan-6-amine framework with the
amidinate unit, which results two tetradentate ligands HL9 and HL10 in Scheme 2.8. These
two ligands can be conveniently prepared by reactions of Me3DAPA with the corresponding
imidoyl chlorides in the presence of triethylamine in toluene solvent (Scheme 2.8) and this
procedure was used earlier in our group to prepare the sterically demanding amidinate ligand
[PhC(N-2,6-iPr2C6H3)2]-.11 They were purified by distillation and isolated as slightly yellow
Chapter 2
20
liquids (isolated yields: HL9, 67%; HL10, 64%), which solidified after cooling to room
temperature. These two compounds were characterized by 1H and 13C NMR spectroscopy
and elemental analysis. The 1H NMR resonances (in C6D6) of NH are found at δ 5.91 and
5.74 ppm for HL9 and HL10, respectively.
Scheme 2.8. Synthesis of Ligands HL9 and HL10.
Scheme 2.9. Synthesis of Ligand HL11 and HL12.
2.3.3.3 N4-Ligands with an Active Hydrogen on the Pendent Amine Nitrogen
Two such ligands were developed based on the Me4DAPA (HL3) fac-tridentate donor
fragment and pendant amide functionalities: Me4DAPA(CH2)2NHtBu (HL11) and
Me4DAPASiMe2NHtBu (HL12) in Scheme 2.9. HL11 was prepared by reaction of Me4DAPA
with N-t-Butyl-α-chloro-acetamide in the presence of a catalytic amount of NaI to form D,
followed by reduction of the carbonyl functionality by reaction with LiAlH4 and subsequent
hydrolysis (Scheme 2.9). It was isolated as a colorless liquid (isolated yield: 36%) after
column chromatography. Ligand HL12 was conveniently synthesized by the lithiation of
Me4DAPA with nBuLi, followed by reaction with N-t-butylamido(dimethyl)chlorosilane
(Scheme 2.9). It was obtained as a colorless liquid (isolated yield: 86%) after Kugelrohr
distillation. HL12 is susceptible to hydrolysis and was stored under dry nitrogen atmosphere.
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
21
These two compounds were characterized by 1H and 13C NMR spectroscopy and elemental
analysis. The 1H NMR resonance (in C6D6) of NH of HL11 was not detected and that of HL12
is present at δ 1.57 ppm.
2.3.4 Synthesis of Tetradentate Ligands with Two Active Hydrogens (on the 6-Amine of Me3DAPA and the Pendant Amine Nitrogen).
Three such ligands were developed: (Me3DAPA)SiMe2NR (H2L13, R = iPr; H2L
14, R = tBu;
and H2L15, R= 2,6-iPr2C6H3) in Scheme 2.10. H2L
13 and H2L14 were conveniently prepared
by the lithiation of Me3DAPA with nBuLi, followed by reaction with the corresponding
alkylamido(dimethyl)chlorosilanes RNHSiMe2Cl (R = iPr for H2L13 and R = tBu for H2L
14)
(Scheme 2.10). Ligand H2L15 was synthesized by reaction of 2,6-iPr2C6H3NHLi with
N-(dimethylchlorosilyl)-1,4,6-trimethyl-1,4-diazepan-6-amine, which was in situ generated
by lithiation of Me3DAPA with nBuLi followed by reaction with excess of SiMe2Cl2
(Scheme. 2.10). These ligands are extremely sensitive to hydrolysis and were mostly used as
the crude product (purity > 95% determined by NMR spectroscopy), obtained by filtration of
the reaction mixture followed by removal of all the volatiles under vacuum.
Scheme 2.10. Synthesis of Ligands H2L13, H2L
14, and H2L15.
Scheme 2.11. Synthesis of Neutral Tetradentate Ligand L16.
2.3.5 Synthesis of Neutral Tetradentate Ligand L16
One such ligand was developed and it was prepared by reaction of Me4DAPA with
pyrolidin-1-yl-α-chloro-acetamide in the presence of catalytic amount of NaI to afford E,
Chapter 2
22
followed by reduction of the carbonyl functionality with LiAlH4 (Scheme 2.11). It was
obtained (isolated yield: 53%) as a colorless liquid after aqueous workup and Kugelrohr
distillation. This compound was characterized by 1H and 13C NMR spectroscopy and
elemental analysis.
2.3.6 Synthesis of Hexadentate Ligands with no or with two Active Hydrogens
Two hexadentate ligands H2L17 and L18 (Scheme 2.12) were developed based on the
1,4-diazepan-6-amine framework. They were conveniently prepared by the condensation of
Me3DAPA with 0.5 equiv of dialdehyde, followed by reduction of the imino functionality
with NaBH4 and aqueous workup, as shown in Scheme 2.12. H2L17 was obtained as a
colorless solid (isolated yield: 51%) after distillation and solidification. L18 was isolated as a
yellow liquid after distillation in 62% isolated yield. These two compounds were
characterized by 1H and 13C NMR spectroscopy and elemental analysis. The 1H NMR
resonance (in C6D6) of NH of H2L17 is found at δ 1.89 ppm and the NMR resonances (in
C6D6) of N=CH are found at δ 8.55 ppm (1H) and δ 156.5 ppm (d, JCH = 156.7 Hz, 13C).
Scheme 2.10. Synthesis of Ligand H2L17 and L18.
2.4 Concluding Remarks
The 1,4,6-trimethyl-1,4-diazepan-6-amine group is suitable as an ancillary ligand
framework for neutral and cationic scandium and yttrium alkyl complexes. It provides a
readily accessible and highly versatile 6-electron donor base for a range of neutral and
anionic tri-, tetra-, and hexadentate ligands. In the following chapters, the application of
these ligands for preparing rare earth organometallics will be investigated and the reactive
and catalytic property of these organometallic complexes will be studied.
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
23
2.5 Experimental Section
General Remarks. All preparations were performed under an inert nitrogen atmosphere,
using standard Schlenk or glovebox techniques, unless mentioned otherwise. Toluene,
pentane, and hexane (Aldrich, anhydrous, 99.8%) were passed over columns of Al2O3
(Fluka), BASF R3-11-supported Cu oxygen scavenger, and molecular sieves (Aldrich, 4 Å).
Diethyl ether and THF (Aldrich, anhydrous, 99.8%) were dried over Al2O3 (Fluka). All
solvents were degassed prior to use and stored under nitrogen. Deuterated solvents (C6D6,
C7D8, THF-d8; Aldrich) were vacuum-transferred from Na/K alloy. NMR spectra were
recorded on Varian Gemini VXR 400 or Varian Inova 500 spectrometers in NMR tubes
equipped with a Teflon (Young) valve. The 1H NMR spectra were referenced to resonances
of residual protons in deuterated solvents. The 13C NMR spectra were referenced to carbon
resonances of deuterated solvents and reported in ppm relative to TMS (δ 0 ppm). GPC
analyses were performed by A. Jekel on a Polymer Laboratories Ltd. (PL-GPC210)
chromatograph with 1,2,4-trichlorobenzene (TCB) as the mobile phase at 150 °C and with
polystyrene references. Elemental analyses were performed at the Microanalytical
Department of the University of Groningen. Benzaldehyde (Fluka, ≥99%), PhSiMe2Cl
(Aldrich, 98%), ethyl formate (Sigma-Aldrich, 97%), LiAlH4 (Aldrich, 95%), NaBH4
(Sigma, ~98%), n-BuLi (Aldrich, 1.6 M in hexane), salicylaldehyde (Aldrich, 98%),
pyrrolidine (Fluka, ≥98%), glyoxal solution (Fluka, ~40% in H2O), and isophthalaldehyde
(Sigma, ≥98%) were used as purchased. N-t-Butyl-α-chloro-acetamide,12
pyrolidin-1-yl-α-chloro-acetamide,12 tBuNHSiMe2Cl,13 pyrrolidin-1-yldimethylsilyl
chloride,14 2-pyrrolidin-1-yl-benzaldehyde,15 N-(2,6-iPr2C6H3)benzimidoyl chloride,16
N-phenylbenzimidoyl chloride16 were prepared according to the literature procedures.
Synthesis of (L)Sc(CH2SiMe3)3 (1). A solution of L (0.371 g, 2.0 mmol) in benzene (20
mL) was added dropwise to a solution of Sc(CH2SiMe3)3(THF)2 (0.902 g, 2.0 mmol) in
benzene (30 mL) while stirring. The mixture was stirred for 30 min. All the volatiles were
removed under reduced pressure and the residue was washed with pentane, yielding the title
compound (0.92 g, 1.87 mmol, 94%) as a slightly yellow solid. 1H NMR (400MHz, C6D6) δ:
3.00 (m, 2H, NCH2), 2.26 (d, 2H, JHH = 13.7 Hz, CCHH), 2.14 (s, 6H, NCH3), 1.91 (s, 6H,
N(CH3)2), 1.52 (m, 2H, NCH2), 1.22 (d, 2H, JHH = 13.7Hz, CCHH), 0.47 (s, 27H, Si(CH3)3),
-0.08 (s, 3H, CCH3), -0.14 (s, 6H, ScCH2). 13C NMR (100.6MHz, C6D6) δ: 68.5 (t, JCH =
137.4 Hz, CCH2), 60.0 (s, MeC), 59.2 (t, JCH = 137.4 Hz, CH2CH2), 50.4 (q, JCH = 138.9 Hz,
N(CH3)2), 42.0 (q, JCH = 138.9 Hz, NCH3), 40.0 (br, ScCH2), 10.8 (q, JCH = 126.2 Hz, CCH3)),
4.7 (q, JCH = 116.5 Hz, Si(CH3)3). Anal. Calcd for C22H56N3Si3Sc: C, 53.72; H, 11.47; N, 8.54.
Found: C, 53.25; H, 11.50; N, 8.41.
Synthesis of (L)Y(CH2SiMe3)3 (2). It was prepared according to the procedure described
for 1 with Y(CH2SiMe3)3(THF)2 (0.990 g, 2.0 mmol) and L (0.371 g, 2.0 mmol) as starting
materials. 2 (1.02 g, 1.9 mmol, 95%) was obtained as an off-white solid. 1H NMR (400MHz,
C6D6) δ: 2.78 (m, 2H, NCH2), 2.19 (d, 2H, JHH = 14.2 Hz, CCH2), 2.11(s, 6H, NCH3), 1.89 (s,
Chapter 2
24
6H, N(CH3)2), 1.51 (m, 2H, NCH2), 1.18 (d, 2H, JHH = 14.2 Hz, CCH2), 0.48 (s, 27H,
Si(CH3)3), -0.11 (s, 3H, CCH3), -0.56 (d, 6H, JYH = 2.8 Hz, YCH2). 13C NMR (100.6MHz,
C6D6) δ: 68.4 (t, JCH = 137.6 Hz, CCH2), 60.9 (s, CCH3)), 58.8 (t, JCH = 140.1 Hz, NCH2),
50.1 (q, JCH = 137.1 Hz, N(CH3)2), 41.4 (q, JCH = 136.1 Hz, NCH3), 36.9 (dt, JCH = 97.9 Hz,
JYC= 35.3, YCH2), 11.6 (q, JCH = 126.7 Hz, CCH3), 5.6 (q, JCH = 117.2 Hz, Si(CH3)3). Anal.
Calcd for C22H56N3Si3Y: C, 49.31; H, 10.53; N, 7.84. Found: C, 49.15; H, 10.45; N, 7.78.
Synthesis of [(L)Sc(CH2SiMe3)2][B(C6H5)4] (3). THF (2 mL) was added to a mixture of
1 (73.8 mg, 150 μmol) and [PhMe2NH][B(C6H5)4] (66.2 mg, 150 μmol). The solution was
homogenised by agitation and allowed to stand for about 20 min. Cyclohexane (3 mL) was
layered carefully on top of the clear, slightly yellow solution. After standing overnight a
white solid had precipitated. The solid was washed with pentane and dried under vacuum to
give the title complex (90.4 mg, 114 mol, 76%) as an off-white powder.1H NMR (400 MHz,
THF-d8) δ: 7.33 (br, 8H, o-H Ph), 6.92 (t, 8H, JHH = 7.48 Hz, m-H Ph), 6.78 (t, 4H, JHH = 7.10
Hz, p-H Ph), 3.04 (d, 2H, JHH = 14.0 Hz, CCH2), 2.95 (m, 2H, NCH2), 2.42 (s, 6H, NCH3),
2.34 (m, 2H, NCH2), 2.30 (s, 6H, N(CH3)2), 2.21 (d, 2H, JHH = 14.0 Hz, CCH2), 0.64 (s, 3H,
CCH3), -0.01 (s, 18H, Si(CH3)3), -0.26 (s, 4H, ScCH2). 13C NMR (100.6MHz, THF-d8) δ:
166.4 (q, JBC = 46.5 Hz, ipso-C Ph), 138.4 (d, JCH = 153.1 Hz, o-C Ph), 127.1 (d, JCH = 152.9
Hz, m-C Ph), 123.3 (d, JCH = 155.6 Hz, p-C Ph), 69.7 (t, JCH = 142.7 Hz, CCH2), 63.5 (s,
CCH3), 60.6 (t, JCH = 142.7 Hz, NCH2), 52.1 (q, JCH = 136.3 Hz, N(CH3)2), 48.4 (br, ScCH2),
43.2 (q, JCH = 137.6 Hz, NCH3), 12.5 (q, JCH = 128.9 Hz, CCH3), 4.8 (q, JCH = 119.3 Hz,
Si(CH3)3).Anal. Calcd for C46H73BN3OSi2Sc: C, 69.41; H, 9.24; N, 5.28. Found: C, 68.60; H,
9.09; N, 5.24.
In situ NMR-scale generation of [(L)Y(CH2SiMe3)2(THF)][B(C6H5)4] (4). THF-d8 (0.6
mL) was added to a mixture of 2 (16.1 mg, 30 μmol) and [PhMe2NH][B(C6H5)4] (13.3 mg,
30 μmol). The obtained solution was transferred into a NMR tube and analyzed with NMR
spectroscopy, which indicated full conversion to the cationic species, SiMe4 and free
PhNMe2.1H NMR (400 MHz, THF-d8) δ: 7.31 (br, 8H, o-H Ph), 6.90 (t, 8H, JHH = 7.47 Hz,
m-C Ph), 6.76 (t, 4H, JHH = 7.07 Hz, p-C Ph), 3.07 (m, 2H, NCH2), 3.03 (m, 2H, CCH2), 2.46
(s, 6H, NCH3), 2.43 (m, 2H, NCH2), 2.31 (s, 6H, NCH3), 2.26 (m, 2H, CCH2), 0.67 (s, 3H,
CCH3), -0.03 (s, 18H, Si(CH3)3), -0.72 (d, 4H, JYH = 2.9 Hz, YCH2). 13C{1H} NMR
(100.6MHz, THF-d8) δ: 166.4 (q, JBC = 46.5 Hz, ipso-C Ph), 138.4 (o-C Ph), 127.1 (m-C Ph),
123.3 (p-C Ph), 69.1 (CCH2), 63.5 (s, CCH3), 59.5 (NCH2), 50.8 (N(CH3)2), 41.5 (NCH3),
41.2 (d, JYC = 41.2 Hz, YCH2), 12.7 (CCH3), 5.3 (Si(CH3)3). Resonances of SiMe4 and
PhNMe2 omitted.
Synthesis of 6-pyrrolidinyl-1,4,6-trimethyl-1,4-diazepine (L1). This reaction was
carried out under aerobic conditions. A mixture of Me3DAPA (4.20g, 26.7 mmol),
1,4-dibromobutane (5.77g, 26.7 mmol), and K2CO3 (3.69 g, 26.7 mmol) in ethanol (80 mL)
was stirred for 36 h at 60 ˚C. H2O (40 mL) was added to the mixture and the resulting
solution was acidified (pH < 1) with 35% HCl solution. All the volatiles were removed under
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
25
reduced pressure and the residue was redissolved in water (40 mL) and then made basic (pH
> 12) with 40% NaOH solution. The mixture was extracted twice with CH2Cl2 (70 mL) and
the combined organic layer was dried over Na2SO4. All the volatiles were removed under
reduced pressure and the residue was purified by Kugelrohr distillation to give the title
compound (3.22 g, 15.2 mmol, 57%) as a colorless liquid. 1H NMR (300 MHz, C6D6) δ: 2.84
and 2.26 (AB system, 4H, CCH2), 2.73 (m, 4H, Py α-H), 2.38 (m, 4H, NCH2), 2.19 (s, 6H,
NCH3), 1.62 (m, 4H, Py β-H), 1.18 (s, 3H, CH3). 13C{1H} NMR (75.4 MHz, C6D6) δ: 66.3
(CCH2), 62.4 (NCH2), 58.6 (CCH3), 49.1 (NCH3), 46.3 (Py α-C), 24.5 (CCH3), 24.1 (Py β-C).
Anal. Calc for C12H25N3: C, 68.20; H, 11.92; N, 19.88. Found: C, 67.41; H, 11.97; N, 19.75.
Synthesis of 1,4,6-trimethyl-N-benzenylmethylene-1,4-diazepa-6-amine (L2). This
reaction was carried out under aerobic conditions. To a 100 mL three-necked flask equipped
with a water condensor and magnetic stirring bar, Me3DAPA (3.15 g, 20 mmol),
benzaldehyde (2.12 g, 20 mmol), and absolute ethanol (60 mL) were added. The solution was
stirred and a drop of formic acid was added to catalyze the reaction. The mixture was heated
at reflux for 6 h and then cooled to room temperature. The mixture was dried over NaSO4 and
all the volatiles were removed under reduced pressure to give a yellow residue. The residue
was purified by Kugelrohr distillation (160 °C, 430 mTorr), yielding the title compound
(3.62 g, 14.8 mmol, 74%) as a yellow liquid. 1H NMR (400MHz, C6D6) δ: 8.57 (s, 1H,
N=CH), 7.83 (d, 2H, JHH = 7.89 Hz, o-H Ph), 7.17 (t, 2H, JHH = 6.65 Hz, m-H Ph), 7.14 (t, 1H,
JHH = 6.88 Hz, p-H, Ph), 2.81 and 2.54 (AB system, 4H, NCH2), 2.44 (m, 4H, NCH2), 2.22 (s,
6H, NCH3), 1.40 (s, 3H, CCH3). 13C{1H} NMR (100.6MHz, C6D6) δ: 156.6 (N=CH), 138.1
(N=CH-C), 130.2 (Ph) , 128.6 (Ph), 128.4 (Ph), 70.0 (CCH2), 63.8 (CCH3), 61.9 (NCH2),
48.8 (N(CH3)2), 26.5 (CCH3). IR(nujol/KBr): 2803(s), 2766 (m), 1643(vs, C=N), 1581(mw),
1308(w), 1287(m), 1122(w), 1218(w), 1122(mw), 1092(s), 1063(w), 959(w), 752(m), 963(m)
cm-1. Anal. Calcd for C15H23N3: C, 73.43; H, 9.45; N, 17.13. Found: C, 72.60; H, 9.36; N,
16.93.
Synthesis of 6-methylamino-1,4,6-trimethyl-1,4-diazepine (HL3). To a 250-mL
two-necked flask equipped with a water condenser, 6-amino-1,4,6-trimethyl-1,4-diazepine
(10.5 g, 66.8 mmol) and ethyl formate (80 mL) were added. The resulting mixture was
refluxed for 2 days and GC indicated that the reaction was complete. Removal of volatiles
under reduced pressure yielded a yellow residue. The residue (12.0 g, 64.8 mmol) was
dissolved in diethyl ether (50 mL) and the resulting solution was slowly added to a
suspension of LiAlH4 (7.1g, 187 mmol) in 200 ml of diethyl ether. The mixture was refluxed
for 4 h, and then water (20 mL) was slowly added. After stirring for another 2 h, Na2SO4 was
added; the salts were filtered off and washed with 5 portions of diethyl ether (50 ml each).
The filtrates were concentrated and the residue distilled to give the title compound (8.5 g,
49.6 mmol, 74%) as a colorless oil (90 °C, 330 mBar). 1H NMR (400MHz, CDCl3) δ: 2.56
(m, 2H, NCH2), 2.40 and 2.26 (AB system, 4H, CCH2), 2.26 (s, 6H, N(CH3)2), 2.22 (s, 3H,
NCH3), 0.84 (s, 3H, CCH3). 13C{1H} NMR (100.5MHz, CDCl3) δ: 67.4 (CCH2), 60.3
Chapter 2
26
(NCH2), 55.1 (CCH3), 48.9 (NCH3), 28.1 (H3CNC), 22.3 (CCH3). Anal. Calcd for C9H21N3:
C, 63.11; H, 12.36; N, 24.53. Found: C: 63.14; H, 12.40; N, 24.12.
Synthesis of 6-dimethylphenylsilylamino-1,4,6-trimethyl-1,4-diazepine (HL4). To a
solution of Me3DAPA (5.03 g, 32 mmol) in diethyl ether (60 mL), n-BuLi solution (20 mL,
32 mmol, 1.6 M in n-hexane) was added dropwise at -40 °C. After addition, the resulting
solution was stirred at room temperature for another 3 h and then cooled to -40 °C.
Chlorodimethylphenylsilane (5.46 g, 32 mmol) was added and the resulting suspension was
stirred overnight at room temperature. The suspension was filtered and the filtrate was dried
under vacuum to give a yellow residue. The residue was purified by distillation (140 °C, 176
mbar), yielding the title compound (7.24 g, 23.6 mmol, 74%) as a colorless liquid. NMR
Spectra indicated that it contains 5% chlorodimethylphenylsilane. 1H NMR (300 MHz, C6D6)
δ: 7.69 (d, 2H, JHH = 7.43 Hz, o-H Ph), 7.25 (t, 2H, JHH = 7.36 Hz, m-H Ph), 7.22 (t, 1H, JHH
= 6.75 Hz, p-H Ph), 2.44 (m, 2H, NCH2), 2.36 (m, 4H, CCH2), 2.26 (m, 2H, NCH2), 2.17 (s,
6H, N(CH3)2), 1.97 (b, 1H, NH), 1.03 (s, 3H, CCH3), 0.38 (s, 6H, Si(CH3)2). 13C NMR (75.4
MHz, C6D6) δ: 142.3 (s, ipso-C Ph), 134.0 (d, JCH = 155.0 Hz, o-C Ph), 129.1 (d, JCH = 157.8
Hz, m-C Ph), 127.9 (d, JCH = 158.5 Hz, p- Ph), 73.6 (t, JCH = 136.3 Hz, CCH2), 61.1 (t, JCH =
130.9 Hz, NCH2), 55.0 (s, CCH3), 49.0 (q, JCH = 132.5 Hz, NCH3), 26.3 (q, JCH = 127.7 Hz,
CCH3), 1.5 (q, JCH = 116.4 Hz, Si(CH3)2). Anal. Calc for [95% C16H29N3Si + 5% C8H11ClSi]:
C, 65.44; H, 9.85; N, 13.69. Found: C, 65.20; H, 10.09; N, 13.50.
Synthesis of tetradentate ligand HL5. This reaction was carried out under aerobic
conditions. To a 100 ml three-necked flask equipped with a water condensor and magnetic
stirring bar, Me3DAPA (3.15 g, 20 mmol), salicylaldehyde (2.44 g, 20 mmol), and absolute
ethanol (60 mL) were added. The solution was stirred and a drop of formic acid was added to
catalyze the reaction. The mixture was heated at reflux for 6 h and then cooled to room
temperature. The mixture was dried over NaSO4 and all the volatiles were removed under
reduced pressure to give a yellow residue. The residue was purified by Kugelrohr distillation
(180 °C, 410 mTorr) yielding 3.42 g (13.1 mmol, 65%) of the title compound. The compound
was characterized with 1H and 13C NMR. 1H NMR (400MHz, C6D6) δ: 8.48 (s, 1H, N=CH),
7.14 (d, 1H, JHH = 7.89 Hz, Ph), 7.08 (t, 1H, JHH = 7.89 Hz, Ph), 7.02 (d, 1H, JHH = 7.42 Hz,
Ph), 6.70 (t, 1H, JHH = 7.42 Hz, Ph), 2.53 and 2.30 (AB system, 4H, NCH2, one overlap with
2.30 multiplets 2.30 (m, 4H, NCH2CH2), 2.11 (s, 6H, NCH3), 1.11 (s, 3H, CCH3). OH
proton was not observed. 13C{1H} NMR (100.6MHz, C6D6) δ: 162.6(O-CH), 162.0 (N=CH),
132.2 (Ph), 131.7 (Ph), 119.8 (N=CH-C), 118.2 (Ph) , 117.7 (Ph), 69.7 (CCH2), 63.1 (CCH3),
61.7 (NCH2), 48.6 (NCH3), 25.0 (CCH3). Anal. Calcd for C15H22N3O: C, 68.93; H, 8.87; N,
16.08. Found: C, 68.55; H, 8.78; N, 15.93.
Synthesis of Ligand HL6. Step 1. This reaction was carried out under aerobic conditions.
To a mixture of NaOH aqueous solution (20 ml, 20%) and CH2Cl2 (60 ml), Me3DAPA (12.0
g, 76.3 mmol) was added. The mixture was cooled to -10 °C and chloroacetyl choloride (7.5
ml, 100 ml) was added dropwise. The resulting mixture was stirred at 0 °C for 1 h. The
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
27
organic layer was separated and the aqueous layer was extracted twice with 50 ml CH2Cl2.
The combined organic layers were dried with Na2SO4 and filtered. Volatiles were removed
under reduced pressure and the residue was purified by crystallization from petroleum ether
to yield compound A (13.4 g, 57.3 mmol, 75%) as a white solid. 1H NMR (300 MHz, CDCl3)
δ: 7.71 (br, 1H, NH), 3.95 (s, 2H, ClCH2), 2.74, 2.55 (AB system, 4H, CCH2), 2.76 (m, 2H,
NCH2), 2.44 (m, 2H, NCH2), 2.35 (s, 6H, NCH3), 1.32 (s, 3H, CCH3). 13C{1H} NMR (75.4
MHz, CDCl3) δ: 165.2 (C=O), 65.9 (ClCH2), 57.8 (CCH2), 55.7 (CCH3), 47.6 (NCH2), 43.2
( NCH3), 23.5 (CCH3).
Step 2. This reaction was carried out under aerobic conditions. To a solution of A (6.20 g,
26.5 mmol) in acetonitrile (40 ml) were added pyrrolidine (3.77 g, 53.0 mmol) and sodium
iodide (15 mg). The resulting suspension was stirred for about 10 h at room temperature and
the completion of the reaction was detected by GC. Water was added to the mixture to make
a clear solution and NaOH (20% eq) was added to make pH ≥ 12. The mixture was then
extracted thrice with diethyl ether (80 ml) and the combined ether lay was washed with brine,
dried with Na2SO4 and filtered. Volatiles were removed under reduced pressure to yield
compound B (6.6 g, 24.6 mmol, 93%) as a slightly yellow liquid. The compound was used
without further purification. 1H NMR (400 MHz, CDCl3) δ: 7.70 (br, 1h, NH), 3.03 (s, 2H,
C(O)CH2), 2.69, 2.54 (AB system, 4H, CCH2), 2.64 (m, 2H, NCH2), 2.56 (m, 4H, α-H Py),
2.40 (m, 2H, NCH2), 2.32 (s, 6H, NCH3), 1.72 (m, 4H, β-H Py), 1.32 (s, 3H, CCH3). 13C{1H}
NMR (100.5 MHz, CDCl3), δ: 170.3 (C=O), 67.1 (C(O)CH2), 59.8 (α-C Py), 59.1 (CCH2),
55.3 (CCH3), 54.1 (NCH2), 48.1 ( NCH3), 23.9 (β-C Py), 23.6 (CCH3).
Step 3. To a solution of B (6.60 g, 24.6 mmol) in di-n-butyl ether (40 ml) was added
lithium aluminium hydride (4.67 g, 123 mmol). The resulting suspension was stirred at 110
°C for 3 h. The suspension was cooled to room temperature and diluted with diethyl ether
(100 ml). Then 14 ml of water was added dropwise carefully with ice-water bath cooling,
which caused vigorous gas evolution. After stirring at room temperature for about 1 h, the
gray suspension became white and Na2SO4 was added to dry the suspension. The solid was
removed by filtration and the volatiles of the filtrate were removed under reduced pressure to
give a slightly yellow oily residue. The residue was purified by Kugelrohr distillation (131
°C, 134 mbar) yielding the title compound HL6 (5.04 g, 19.8 mmol, 81%) as a colorless
liquid. 1H NMR (400 MHz, C6D6) δ: 2.69 (m, 2H, NCH2), 2.62 (m, 2H, NCH2), 2.54, 2.35
(AB system, 4H, CCH2), 2.42 (m, 6H, NCH2 and α-H Py), 2.30 (m, 2H, NCH2), 2.20 (s, 6H,
NCH3), 1.59 (m, 4H, β-H Py), 1.05 (s, 3H, CCH3). NH signal was not observed. 13C NMR
(100.5 MHz, C6D6) δ: 68.8 (t, JCH = 128.8 Hz, CCH2), 61.4 (t, JCH = 131.5 Hz, α-C Py), 57.4
(t, JCH = 131.1 Hz, NCH2), 55.8 (s, CCH3), 54.4 (t, JCH = 134.8 Hz, NCH2), 49.2 (q, JCH =
133.0 Hz, NCH3), 24.0 (q, JCH = 124.8 Hz, CCH3), 23.9 (t, JCH = 132.0 Hz, β-C Py). Anal.
Calc for C14H30N4: C, 66.09; H, 11.89; N, 22.02. Found: C, 66.06; H, 12.24; N, 21.90.
Synthesis of Ligand HL7. Step 1. This reaction was carried out under aerobic conditions.
To a 100 mL three-necked flask equipped with a magnetic stirring bar and a water condenser,
Chapter 2
28
Me3DAPA (4.72 g, 30 mmol), 2-pyrrolidin-1-ylbenzaldehyde (5.26 g, 30 mmol), and
absolute ethanol (60 mL) were added. The mixture was stirred and a drop of formic acid was
added to catalyze the reaction. The resulting solution was refluxed for 8 h and then cooled to
room temperature. The mixture was dried over Na2SO4 and filtered. All the volatiles of the
filtrate were removed under reduced pressure. The residue was purified by Kugelrohr
distillation (170 ºC, 320 mTorr) to give C (7.74 g, 24.6 mmol, 82%) as a yellow liquid, which
solidified upon standing at room temperature overnight. 1H NMR (400 MHz, C6D6) δ: 8.99 (s,
1H, N=CH), 8.34 (dd, 1 H, JHH = 7.7 Hz, JHH = 1.8 Hz, 6-H Ph), 7.19 (ddd, 1H, JHH = 8.1 Hz,
JHH = 7.3 Hz, JHH = 1.8 Hz, 4-H Ph), 6.93 (t, 1H, JHH = 7.3 Hz, 5-H Ph), 6.78 (d, 1H, JHH = 8.1
Hz, 3-H Ph), 3.04 (m, 4H, α-H Py), 2.85 and 2.60 (2H, AB system, CCH2), 2.43 (m, 4H,
NCH2), 2.23 (s, 6H, NCH3), 1.55 (m, 4H, β-H, Py), 1.45 (s, 3H, CCH3). 13C{1H} NMR
(100.5 MHz, C6D6) δ: 156.4 (N=CH), 150.5 (Py-C), 130.4 (Ph), 129.1 (Ph), 128.4 (Ph),
120.4 (Ph), 115.8 (Ph), 70.0 (CCH2), 63.7 (CCH3), 61.9 (NCH2), 52.8 (α-C Py), 48.8 (NCH3),
27.0 (β-C, Py), 25.3 (CCH3).
Step 2. This reaction was carried out under aerobic conditions. Compound C (4.09 g, 13
mmol) was dissolved in methanol (50 mL) and NaBH4 (1.50 g, 40 mmol) was added. The
resulting mixture was stirred at room temperature for 4 h and then Na2B4O7 (3 g) was added.
H2O (50 mL) was added to make a clear solution and the mixture was extracted thrice with
CH2Cl2 (60 mL). The combined organic layer was dried over Na2SO4 and filtered. All the
volatiles of the filtrate were removed under reduced pressure and the residue was purified by
Kugelrohr distillation (190 ºC, 340 mTorr), yield the title compound (3.58 g, 11.3 mmol,
87%) as a colorless liquid. 1H NMR(400 MHz, C6D6) δ: 7.66 (d, 1 H, JHH = 7.4 Hz, Ph), 7.18
(t, 1H, JHH = 7.5 Hz, Ph), 7.00 (t, 1H, JHH = 7.3 Hz, Ph), 6.91 (d, 1H, JHH = 7.8 Hz, Ph), 3.87
(s, 2H, PhCH2), 3.11 (m, 4H, α-H Py), 2.58 and 2.35 (2H, AB system, CCH2), 2.41 (m, 4H,
NCH2), 2.28 (m, 2H, NCH2), 2.18 (s, 6H, NCH3), 1.65 (m, 4H, β-H, Py), 1.08 (s, 3H, CCH3).
The resonance of NH was not observed. 13C{1H} NMR (100.5 MHz, C6D6) δ: 149.3 (Py-C),
133.7 (Ph), 131.0 (Ph), 127.4 (Ph), 127.4 (Ph), 117.1 (Ph), 68.7 (CCH2), 61.2 (NCH2), 56.2
(CCH3), 51.9 (α-C Py), 49.1 (NCH3), 43.6 (PhCH2N), 25.0 (β-C, Py), 23.9 (CCH3).
Synthesis of Ligand HL8. To a solution of Me3DAPA (5.03 g, 32 mmol) in diethyl ether
(100 mL), n-BuLi solution (20 mL, 32 mmol, 1.6 M in n-hexane) was added dropwise at 0 ̊ C.
After addition, the mixture was stirred at room temperature for another 3 h and then cooled to
0˚C. Pyrrolidin-1-yldimethylsilyl chloride (5.24 g, 32 mmol) was added in one portion and
the resulting suspension was stirred at room temperature for another 6 h. All the volatiles of
the suspension were removed under vacuum and the residue was suspended in pentane (100
mL). The suspension was filtered and all the volatiles of the filtrate were removed under
reduced pressure. The residue was purified by distillation (163 ˚C, 232 mbar), yielding the
title compound (6.90 g, 24.3 mmol, 76%) as a colorless liquid. 1H NMR (400MHz, C6D6) δ:
3.00 (m, 4H, α-H Py), 2.49 and 2.40 (AB system, 4H, CCH2), 2.46 (m, 2H, NCH2), 2.43 (m,
2H, NCH2), 2.23 (s, 6H, NCH3), 1.76 (br, 1H, NH), 1.60 (m, 4H, β-H Py), 1.18 (s, 3H, CCH3),
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
29
0.19 (s, 6H, Si(CH3)2). 13C NMR (100.4 MHz, C6D6) δ: 74.0 (t, JCH = 132.1 Hz, CCH2), 61.4
(t, JCH = 133.3 Hz, α-C Py), 54.4 (s, CCH3), 49.2 (q, JCH = 133.0 Hz, NCH3), 46.8 (t, JCH =
136.9 Hz, NCH2), 27.2 (t, JCH = 129.7 Hz, β-C Py), 25.8 (q, JCH = 127.1 Hz, CCH3), 6.2 (q,
JCH = 116.9 Hz, Si(CH3)2). Anal. Calc for C16H29N3Si: C, 59.10; H, 11.34; N, 19.69. Found:
C, 58.88; H, 11.35; N, 19.18.
Synthesis of Ligand HL9. This reaction was carried out under aerobic conditions. To a
100 mL two-necked flask equipped with a magnetic stirring bar and a water condenser,
Me3DAPA (4.72 g, 30 mmol), N-phenylbenzimidoyl chloride (6.47g, 30 mmol),
triethylamine (3.05 g, 30 mmol) and toluene (60 mL) were added. The mixture was refluxed
for 12 h and then cooled to room temperature. Concentrated HCl (aq) (10 mL) and water
(100 mL) were added and the mixture was then extracted twice with diethyl ether (100 mL).
The aqueous solution was made basic (pH > 12) with NaOH solution (aq, 20%) and then
extracted thrice with diethyl ether (100 mL). The combined ether layer was washed with
saturated NaCl solution and then dried over Na2SO4. Volatiles were removed under reduced
pressure to give a brown residue (8.21 g), which was purified by distillation (210 ºC, 320
mTorr), yielding the title compound (6.72 g, 20 mmol, 67%) as a yellow oil, which solidified
upon standing at room temperature overnight. 1H NMR (400 MHz, C6D6) δ: 7.40 (d, 2H, JHH
= 7.72 Hz, o-Ph), 7.05 (t, 2H, m-Ph), 6.88 (m, 5H, Ph overlap), 6.76 (t, 1H, JHH = 7.37 Hz,
p-Ph), 5.91 (s, 1H, NH), 3.10, 2.38 (AB system, 4H, CCH2), 2.56 (m, 2H, NCH2), 2.19 (s, 6H,
NCH3), 2.16 (m, 2H, NCH2), 1.70 (s, 3H, CCH3). 13C{1H} NMR (100.5 MHz, C6D6) δ: 157.0
(NCN), 152.3 (ipso-Ph), 137.4 (ipso-Ph), 129.0 (Ph), 128.7 (p-Ph) 128.6 (Ph), 128.4 (Ph),
123.4 (m-Ph), 121.0 (p-Ph), 66.2 (CCH2), 58.4 (NCH2), 56.6 (CCH3), 48.1 (NCH3), 24.1
(CCH3).
Synthesis of Ligand HL10. It was synthesized by following the procedure described for
HL9. Me3DAPA (4.72, 30 mmol), N-(2,6-iPr2C6H3)benzimidoyl chloride (8.99 g, 30 mmol),
and triethylamine (3.05 g, 30 mmol) were used as starting materials. HL10 (8.03 g, 19.1
mmol, 64%) was obtained as a yellow solid. 1H NMR (300 MHz, C6D6) δ: 7.37 (d, 2H, JHH =
7.25 Hz, o-H Ph), 7.05 (m, 3H, Ph), 6.86 (m, 3H, Ph), 5.74 (s, 1H, NH), 3.39 (septet, 2H, JHH
= 6.9 Hz, CH(CH3)2), 3.09 and 2.52 (AB system, 4H, CCH2), 2.55 (m, 2H, NCH2), 2.22 (s,
6H, NCH3), 2.19 (m, 2H, NCH2), 1.75 (s, 3H, CCH3), 1.31 (d, 6H, JHH = 6.9 Hz, CH(CH3)2),
1.09 (d, 6H, JHH = 6.9 Hz, CH(CH3)2). 13C{1H} NMR (75.4 MHz, C6D6) δ: 177.8 (NCN),
153.8 (Ph), 146.7 (Ph), 138.6 (Ph), 128.8 (Ph) 128.1 (Ph), 123.0 (Ph), 122.3 (Ph), 121.0
(p-Ph), 66.2 (CCH2), 58.4 (NCH2), 56.6 (CCH3), 48.1 (NCH3), 24.1 (CCH3). 66.6 (CCH2),
58.8 (NCH2), 56.0 (CCH3), 48.2 (NCH3), 28.7 (CH(CH3)2), 28.6 (CH(CH3)2), 25.0
(CH(CH3)2), 22.5 (CCH3).
Synthesis of Ligand HL12. To a solution of HL3 (4.11 g, 24 mmol) in diethyl ether (100
mL), was added n-BuLi solution (15 mL, 24 mmol, 1.6 M in n-hexane) dropwise at 0 ˚C.
After addition, the solution was stirred at room temperature for another 3 h and then cooled
to 0˚C. (tButylamino)dimethylsilyl chloride (3.98 g, 24 mmol) was added in one portion and
Chapter 2
30
the resulting suspension was stirred at room temperature for another 6 h. The suspension was
filtered and all the volatiles were removed under reduced pressure. The residue was purified
by distillation (165 ˚C, 287 mTorr), yielding the title compound (6.20 g, 20.6 mmol, 86%) as
a colorless liquid. 1H NMR (300MHz, C6D6) δ: 2.99 and 2.28 (AB system, 4H, CCH2), 2.64
(s, 3H, NCH3), 2.44 (m, 2H, NCH2), 2.31 (m, 2H, NCH2), 2.20 (s, 6H, NCH3), 1.57 (br, 1H,
NH), 1.38 (s, 3H, CCH3), 1.21 (s, 9H, NC(CH3)3), 0.30 (s, 6H, Si(CH3)2). 13C NMR (75.4
MHz, C6D6, δ): 69.2 (t, JCH = 132.5 Hz, CCH2), 62.3 (t, JCH = 131.4 Hz, NCH2), 60.5 (s,
C(CH3)3), 49.2 (q, JCH = 135.2 Hz, NCH3), 48.8 (s, CCH3), 33.9 (q, JCH = 124.6 Hz, NCH3),
31.1 (q, JCH = 133.3 Hz, C(CH3)3), 26.9 (q, JCH = 127.1 Hz, CCH3), 6.2 (q, JCH = 117.6 Hz,
Si(CH3)2). Anal. Calc for C15H36N4Si: C, 59.94; H, 12.07; N, 18.64. Found: C, 59.69; H,
12.09; N, 18.24.
Synthesis of ligand H2L13. To a solution of Me3DAPA (5.03 g, 32.0 mmol) in diethylether
(80 ml), was added dropwise n-BuLi solution (20 ml, 32 mmol) at 0 ºC. After completion, the
resulting yellowish solution was stirred at 0 ºC for 1 h and then at room tempertature for 3 h.
iPrN(H)Si(Cl)Me2 (4.85 g, 32 mmol) was added in one portion at 0 ºC and white precipitate
formed immediately. The resulting suspension was stirred at room temperature for 3 h and all
the volatiles were removed under reduced pressure. The residue was dissolved in pentane (70
ml) and filtered. The filtrate was dried under vacuum to yield the title compound (7.47 g,
27.4 mmol, 86%) as a yellow oil, which was used without further purification. 1H NMR (300
MHz, C6D6) δ: 3.16 (m, 1H, NCH(CH3)2), 2.51, 2.43 (AB system, 4H, CCH2), 2.47 (m, 2H,
N CH2), 2.33 (m, 2H, NCH2), 2.24 (s, 6H, N(CH3)2), 1.73 (b, 1H, NH), 1.26 (s, 3H, CCH3),
1.05 (d, 6H, JHH = 6.3 Hz, CH(CH3)2), 0.15 (s, 6H, Si(CH3)2). One resonance of NH was not
observed. 13C{1H}NMR (75.4 MHz, C6D6) δ: 74.0 (CCH2), 61.4 (NCH2), 54.6 (CCH3), 49.2
(NCH3), 42.6 (NCH), 28.1 (CH(CH3)2), 26.0 (CCH3), 2.0 (Si(CH3)2).
Synthesis of ligand H2L14. It was made by following the procedure described for H2L
11.
Me3DAPA (5.03 g, 32.0 mmol), n-BuLi solution (20 ml, 32 mmol), and tBuN(H)SiMe2Cl
(5.30 g, 32 mmol) were used as starting materials. The same workup procedure afforded the
title compound (7.32 g, 25.5 mmol, 80%) as a yellow oil. 1H NMR (400 MHz, C6D6) δ:
2.51-2.29 (m, 4H, NCH2), 2.45 and 2.22 (AB system, 4H, CCH2), 2.22 (s, 6H, NCH3), 1.62
(broad, 1H, SiNH), 1.23 (s, 3H, CCH3), 1.20 (s, 9H, C(CH3)3), 0.77 (broad, 1H, SiNH), 0.19
(s, 6H, Si(CH3)2). Anal. Calcd for C13H34N4Si: C, 58.68, H, 11.96, N, 19.55. Found: C, 58.22,
H, 11.96, N, 19.34.
Synthesis of ligand H2L15. To a solution of 1,4,6-trimethyl-1,4-diazepan-6-amine (7.86 g,
50 mmol) in diethyl ether (100 ml) at 0 ˚C, was added a solution of nBuLi (20 ml, 50 mmol,
2.5 M in hexane). The reaction mixture was stirred for 3 h at room temperature and then
cooled to 0 ˚C. Dichlorodimethylsilane (25.8 g, 200 mmol) was added in one portion and the
resulting mixture was then stirred for 3 h at room temperature. All the volatiles were
removed under reduced pressure and the residue was extracted with pentane (2×60 ml). The
obtained extract was dried under vacuum and the residue was purified by distillation (350
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
31
mTorr, 140 ºC) to yield N-(chlorodimethylsilyl)-1,4,6-trimethyl-1,4-diazepan-6-amine (9.47
g, 38 mmol, 76%) as a colorless liquid. 1H NMR (300 MHz, C6D6) δ: 2.67 (br, 1H, NH), 2.43
(m, 2H, NCH2), 2.38 (d, 4H, JHH = 4.3 Hz, CCH2), 2.20 (m, 2H, NCH2), 2.19 (s, 6H, NCH3),
1.14 (s, 3H, CCH3), 0.37 (s, 6H, SiCH3). 13C NMR (76.4 MHz, C6D6) δ: 72.1 (t, JCH = 131.7
Hz, CCH2), 60.2 (t, JCH = 130.4 Hz, NCH2), 55.1 (s, CCH3), 48.7 (q, JCH = 133.8 Hz, NCH3),
25.7 (q, JCH = 121.5 Hz, CCH3), 4.8 (q, JCH = 119.3 Hz, SiCH3).
To a solution of N-(chlorodimethylsilyl)-1,4,6-trimethyl-1,4-diazepan-6-amine (4.75 g,
19.2 mmol) in THF (20 ml), was added a solution of ArNHLi (Ar = 2,6-iPr2C6H3) (3.48 g,
19.2 mmol) at 0 ˚C and the resulting mixture was stirred for 3 h at room temperature. The
volatiles were removed under vacuum and the residue was extracted with pentane (60 ml).
The obtained extract was dried under vacuum to yield the title compound (5.82 g, 14.9 mmol,
78%) as an yellow oil. 1H NMR (300 MHz, C6D6) δ: 7.14 (d, 2H, JHH = 6.42 Hz, m-H-Ph),
7.07 (m, 1H, p-H-Ph), 3.68 (sept, 2H, JHH = 6.87 Hz, CH(CH3)2), 2.73 (br, 1H, NH), 2.44 (m,
2H, NCH2), 2.41 (d, 4H, JHH = 7.68 Hz, CCH2), 2.28 (m, 2H, NCH2), 2.21 (s, 6H, NCH3),
1.21 (d, 12H, JHH = 6.93 Hz, CH(CH3)2), 1.18 (s, 3H, CCH3), 0.22 (s, 6H, SiCH3). 13C NMR
(76.4 MHz, C6D6) δ: 143.3 (s, o-C-Ph), 140.6 (s, ipso-C-Ph), 123.4 (d, JCH = 128.6 Hz,
m-C-Ph), 123.3 (d, JCH = 128.6 Hz, p-C-Ph), 73.4 (t, JCH = 129.6 Hz, CCH2), 60.9 (t, JCH =
131.4 Hz, NCH2), 54.6 (s, CCH3), 49.1 (q, JCH = 133.0 Hz, NCH3), 28.4 (d, JCH = 127.0 Hz,
CH(CH3)2), 26.4 (q, JCH = 125.2 Hz, CCH3), 23.9 (q, JCH = 126.1 Hz, CH(CH3)2), 2.3 (q, JCH
= 117.8 Hz, SiCH3).
Synthesis of neutral tetradentate ligand L16. This reaction was carried out under aerobic
conditions. To a solution of crude HL3 (3.26 g, 18.3 mmol) in acetonitrile (35 mL), was
added 1-(chloroacetyl)pyrrolidine (2.73 g, 18.3 mmol) and NaI (30 mg) and the resulting
mixture was refluxed for 4 h. The reaction mixture was made basic (pH > 12) with aqueous
NaOH solution (20%) and extracted with CH2Cl2 (2 × 50 mL). The combined organic
solution was dried over Na2SO4 and filtered. All the volatiles of the filtrate were removed
under vacuum. The residue was dissolved in THF (20 mL) and the resulting solution was
added to a suspension of LiAlH4 (2.6 g) in di-n-butylether (40 mL). The suspension was
heated at 100 ºC for 2 h and then diluted with diethyl ether (100 mL). H2O (6 mL) was
carefully added and the mixture was dried over Na2SO4 and filtered. All the volatiles were
removed under vacuum and the residue was distilled (340 mTorr, 160º), yielding the title
compound (2.41 g, 9.0 mmol, 49%) as a colorless liquid. 1H NMR (300 MHz, C6D6) δ: 3.00
(m, 2H, CH2-Bridge), 2.82 and 2.24 (AB system, 4H, NCH2), 2.65 (m, 2H, CH2-Bridge),
2.50 (m, 4H, α-H Py), 2.41 (m, 2H, NCH2), 2.34 (s, 3H, NCH3), 2.29 (m, 2H, NCH2), 2.18 (s,
6H, NCH3), 1.63 (m, 4H, β-H Py), 1.16 (s, 3H, CCH3). 13C{1H} NMR (75.4 MHz, C6D6) δ:
66.6 (CCH2), 62.5 (α-C Py), 60.4 (CCH3), 57.5 (NCH2), 54.9 (NCH2), 51.0 (NCH2), 49.0
(NCH3), 36.8 (NCH3), 25.0 (β-C Py), 24.0 (CCH3).
Synthesis of hexadentate ligand H2L17. This reaction was carried out under aerobic
conditions. Aqueous 40wt% glyoxal solution (2.5 g, 17.2 mmol) was added dropwise to
Chapter 2
32
1,4,6-trimethyl-1,4-diazepan-6-amine (5.4 g, 34.4 mmol) at 0 ºC. After addition, the mixture
was stirred for 30 min at room temperature and then H2O (30 mL) was added. The solution
was extracted with CH2Cl2 (2 × 50 mL). The combined organic solution was dried over
Na2SO4 and filtered. All the volatiles of the filtrate were removed under vacuum. The residue
was dissolved in methanol (80 mL) and then NaBH4 (1.4 g, 37 mmol) was added. The
mixture was stirred for 2 h at room temperature and H2O (50 mL) was added. The solution
was made basic (pH > 12) with aqueous NaOH solution (20%) and then extracted with
CH2Cl2 (3 × 50 mL). The combined organic solution was dried over Na2SO4 and filtered. All
the volatiles of the filtrate were removed under vacuum and the residue was distilled,
yielding the title compound (3 g, 8.8 mmol, 51%) as a colorless liquid, which solidified upon
standing overnight at room temperature. 1H NMR (300 MHz, C6D6) δ: 2.60 (m, 4H,
NCH2-bridge), 2.44 and 2.25 (AB system, 8H, NCH2), 2.37 (m, 4H, NCH2), 2.24 (m, 4H,
NCH2), 2.15 (s, 12H, NCH3), 1.89 (m, 2H, NH), 0.94 (s, 6H, CCH3). 13C NMR (75.4 MHz,
C6D6) δ: 68.7 (t, JCH = 130.2 Hz, CCH2), 61.3 (t, JCH = 132.2 Hz, NCH2), 55.8 (CCH3), 49.1
(q, JCH = 134.1 Hz, NCH3), 43.3 (t, JCH = 131.9 Hz, NCH2-Bridge), 24.0 (q, JCH = 125.7 Hz,
CCH3).
Synthesis of hexadentate ligand L18. This reaction was carried out under aerobic
conditions. To a 100 mL two-necked flask equipped with a magnetic stirring bar and a water
condenser, isophthalaldehyde (2.01 g, 15 mmol), 1,4,6-trimethyl-1,4-diazepan-6-amine
(4.72 g, 30 mmol), and absolute ethanol (60 mL) were added. A few drops of formic acid
were added to catalyze the reaction. The mixture was refluxed for 24 h and then cooled to
room temperature. The mixture was dried over NaSO4 and all the volatiles were removed
under reduced pressure to give a yellow residue. The residue was purified by Kugelrohr
distillation (250 °C, 230 mTorr), yielding the title compound (3.84 g, 9.3 mmol, 62%) as a
yellow liquid. 1H NMR (300 MHz, C6D6) δ: 8.55 (s, 2H, N=CH), 8.39 (s, 1H, 2-H Ph), 7.87
(d, 2H, JHH = 7.7 Hz, 4,6-H Ph), 7.18 (t, 1H, JHH = 7.7 Hz, 5-H Ph), 2.79 and 2.52 (AB
system, 8H, NCH2), 2.42 (m, 8H, NCH2), 2.20 (s, 12H, NCH3), 1.37 (s, 6H, CCH3). 13C
NMR (75.4 MHz, C6D6) δ: 156.5 (d, JCH = 156.7 Hz, N=CH), 138.4 (dd, JCH = 7.5 Hz, JCH =
11.8 Hz, 1,3-C Ph), 129.8 (d, JCH = 160.5 Hz, 4,6-C Ph), 128.8 (d, JCH = 160.4 Hz, 2-C Ph),
128.6 (d, JCH = 159.0 Hz, 5-C Ph), 70.0 (t, JCH = 135.3 Hz, CCH2), 63.9 (CCH3), 61.9 (t, JCH
= 131.2 Hz, NCH2), 48.8 (q, JCH = 135.3 Hz, NCH3), 26.5 (q, JCH = 126.2 Hz, CCH3).
Structure Determination of 1. Suitable single crystals of 1 were obtained by
recrystallization from a toluene/hexane mixture. Crystals were mounted on a glass fiber
inside a drybox, and transferred under inert atmosphere to the cold nitrogen stream of a
Bruker SMART APEX CCD diffractometer. Intensity data were collected with Mo Kα
radiation (λ = 0.71073 Å). Intensity data were corrected for Lorentz and polarization effects.
A semiempirical absorption correction was applied, based on the intensities of
symmetry-related reflections measured at different angular settings (SADABS14). The
structures were solved by Patterson methods and extension of the models was accomplished
Synthesis of Ancillary Ligands Based on the 1,4-Diazepan-6-amine Framework
33
by direct methods applied to difference structure factors, using the program DIRDIF15. In a
subsequent difference Fourier synthesis all hydrogen atoms were located, of which the
positional and isotropic displacement parameters were refined. All refinements and
geometry calculations were performed with the program packages SHELXL16 and
PLATON17. Crystallographic data and details of the data collections and structure
refinements of 1 is as following: C22H56N3Si3Sc, M = 491.92, monoclinic, space group P21/c,
a = 18.418(1), b = 17.990(1), c = 18.694(1) Å, β = 95.799(1)°, V = 6162.4(6) Å3, Z = 8, Dx =
1.060 gcm-3, F(000) = 2176, μ = 3.68 cm-1, λ(MoKα) = 0.71073 Å, T = 100(1) K, 41674
reflections measured, GooF = 0.964, wR(F2) = 0.1084 for 12024 unique reflections and 971
parameters and R(F) = 0.0544 for 7135 reflections obeying Fo ≥ 4.0σ(Fo) criterion of
observability.
2.6 References:
1. (a) Arndt, S.; Okuda, J. Adv. Synth. Catal. 2005, 347, 339. (b) Zeimentz, P. M.; Arndt, S.;
Elvidge, B. R.; Okuda, J. Chem. Rev. 2006, 106, 2404.
2. (a) Hajela, S.; Schaefer, W. P.; Bewcaw, J. E. J. Organomet. Chem. 1997, 532, 45. (b)
Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2001,
637. (c) Lawrence, S. C.; Ward, B. D.; Dubberley, S. R.; Kozak, C. M.; Mountford, P. Chem.
Commun. 2003, 2880. (d) Ward, B. D.; Bellemin-Laponnaz, S.; Gade, L. H. Angew. Chem.
Int. Ed. 2005, 44, 1668.
3. Peralta, R. A.; Neves, A.; Bortoluzzi, A. J.; Casellato, A.; dos Anjos, A.; Greatti, A.; Xavier,
F. R.; Szpoganicz, B. Inorg. Chem., 2005, 44, 7690.
4. Appel, A. C. M.; Hage, R.; Russell, S. W.; Tetard, D. WO 01/85717 A1.
5. Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973, 126.
6. (a) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun.
2001, 637. (b) Bambirra, S.; van Leusen, D.; Tazelaar, C. G. J.; Meetsma, A.; Hessen, B.
Organometallics 2007, 26, 1014.
7. (a) Kreher, R. P.; Hildebrand, T. Natureforsch., B: Chem. Sci. 1988, 43, 125. (b) Kreher, R.
P.; Sewarte-Ross, G.; Vogt, G. Chem. Ber. 1990, 123, 1719. (C) Reddy, K. S.; Solà, L.;
Moyano, A.; Pericàs, M. A.; Piera, A. J. Org. Chem. 1999, 64, 3969. (d) Bertrand, S.;
Hoffmann, N.; Pete, J-P. Eur. J. Org. Chem. 2000, 2227.
8. (a) Emslie, D. J. H.; Piers, W. E.; Parvez, M.; McDonald, R. Orgnaometallics 2002, 21, 4226.
(b) Emslie, D. J. H.; Piers, W. E.; Parvez, M. Dalton Trans. 2002, 293. (c) Emslie, D. J. H.;
Piers, W. E.; Parvez, M. Dalton Trans. 2003, 2615.
9. (a) Edelmann, F. Coord. Chem. Rev. 1994, 137, 403. (b) Barker, J.; Kilner, M. Coord. Chem.
Rev. 1994, 133, 219. (c) Bailey, P. J.; Pace, S. Coord. Chem.Rev. 2001, 214, 91. (d)
Chapter 2
34
Kissounko, A.; Zabalov, M. V.; Brusova, G. P.; Lemenovskii, D. A. Russ.Chem.Rev. 2006,
75, 351–374. (e) Edelmann, F. T. Adv. Organomet. Chem. 2008, 57, 183.
10. (a) Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A. C.; Meetsma, A.; Hessen, B.; Teuben, J.
H. Orgnaometallics 2000, 19, 3197. (b) Bambirra, S.; Meetsma, A.; Hessen, B.; Teuben, J. H.
Organometallics 2001, 20, 782. (c) Wang, J.; Sun, H.; Yao, Y.; Zhang, Y.; Shen, Q.
Polyhedron 2008, 27, 1977. (d) Wang, J.; Yao, Y.; Zhang, Y.; Shen, Q. Inorganic Chemistry
2008, 49, 744.
11. Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2003,
522.
12. Speziale, A. J.; Hamm, P. C. J. Am. Chem. Soc. 1956, 78, 2556.
13. Grandini, C.; Camurati, I.; Guidotti, S.; Mascellani, N.; Resconi, L.; Nifant’ev, I. E.;
Kashulin, I. A.; Ivchenko, P. V.; Mercandelli, P.; Sironi, A. Organometallics 2004, 23, 344.
14. Tamao, K.; Nakaji, E.; Ito, Y. Tetrahedron 1988, 44, 3997.
15. Nijhuis, W. H. N.; Verboom, W.; Abu El-Fadl, A.; Harkema, S.; Reinhoudt, D. N. J. Org.
Chem. 1989, 54, 199.
16. Ugi, I.; Beck, F.; Fetzer, U. Chem. Ber. 1962, 95, 126.
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
35
Chapter 3 Organo Rare Earth Metal Complexes with fac-κ3
Nitrogen-based Neutral Ligand Precursors
3.1 Introduction
Neutral and cationic rare earth metal alkyl species are catalytically active for a range of
transformations,1 such as olefin polymerization,2 dimerization of alkynes,3 and the
hydroamination,4 hydrophosphination,5 or hydrosilylation6 of alkenes. Neutral
nitrogen-based facial tridentate ancillary ligands, such as 1,4,7-trimethyltriazacyclononane,
tris(pyrazolyl)methane, and tris(oxazolinyl)methane, have been reported to stabilize these
species, but rare earth metal compounds bearing these ligands were reported only for metals
in the small to medium ionic size range (Sc, Y, Dy-Lu),7 mainly due to the availability of the
corresponding isolated trialkyl starting materials M(CH2SiMe2R)3(THF)n (M = Sc, Y, Dy-Lu;
R = Me or Ph; n= 1-2) for these metals only. Recent isolation of the tribenzyl complex of
lanthanum (the largest rare earth metal), La(CH2Ph)3(THF)3, as well as its Sc and Lu
congeners,8 offers an opportunity to investigate the organometallic chemistry with this type
of neutral κ3 nitrogen-based ancillary ligands over the full size range of the rare earth metals.
In chapter 1, we introduced the 1,4,6-trimethyl-1,4-diazepan-6-amine moiety as
ancillary ligand framework for neutral and cationic Sc and Y complexes and two neutral
ligands (L1 and L2 in Chart I) derived from this ligand motif were synthesized. In this chapter,
we describe their application in synthesis of neutral and cationic rare earth metal
orgnaometallics, using the metals Sc, Y and La (representing respectively the smallest, a
typical intermediate size and the largest metal in rare earth metal series). The synthesized
neutral and cationic complexes supported by L1 were also studied as catalysts for the
hydroamination/cyclization of two commonly used standard substrates,
2,2-diphenyl-4-pentenylamine (S1) and N,N-methyl-4-pentenylamine (S2). Earlier, it was
shown that the nature of monoanionic ancillary ligands can have a significant influence on
the relative rate of conversion for hydroamination/cyclization reactions catalyzed by neutral
rare earth metal complexes versus their corresponding cationic species.9 In this chapter we
have probed the dependence of the relative catalyst performance of neutral and cationic
species on the metal size for the neutral N3 ancillary ligand system.
Chart I. Ligands Employed in This Chapter.
Chapter 3
36
3.2 Synthesis of Neutral Organo Rare Earth Metal Complexes
3.2.1 Synthesis and Characterization of Trialkyl Complexes (L1)M(CH2SiMe3)3 (M = Sc, Y)
Reactions of the group 3 metal trialkyls M(CH2SiMe3)3(THF)2 (M = Sc and Y) with
ligand L1 in toluene afforded complexes (L1)M(CH2SiMe3)3 (M = Sc, 5; M = Y, 6)10 as
crystalline materials after recrystallization from toluene/n-hexane solution (isolated yields:
5, 70%;6, 61%), as shown in Scheme 3.1. When the reactions were performed in C6D6,
complexes 5 and 6 were formed quantitatively as seen by 1H NMR spectroscopy. The six
methylene protons of the three trimethylsilylmethyl groups are equivalent for both
complexes on the NMR time scale. The M-CH2 resonances (C6D6, 25 ºC) for 5 are found at
δ -0.11 ppm (1H) and δ 39.7 ppm (13C), for 5 at δ -0.54 ppm (d, JYH = 2.8 Hz) and δ 39.7
ppm (dt, JYC = 36.2 Hz, JCH = 96.5 Hz) respectively. For both complexes in C6D6, the
1,4-diazepane and pyrrolidinyl ring methylene protons are diastereotopic, indicating that in
solution ligand L1 is κ3 bound to M(CH2SiMe3)3 fragment.
Scheme 3.1. Synthesis of Trialkyl Complexes 5 and 6.
Figure 3.1. Structures of Complexes 5 (left) and 6 (right). All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
37
The structures of (isomorphous) 5 and 6 were determined by single-crystal X-ray
diffraction. Their molecular structures are shown in Figure 3.1. The geometrical data are
compiled in Table 3.1. The metal center in both 5 and 6 has approximately octahedral
coordination geometry with a facially coordinated N3 ligand and three alkyl ligands. In
overall geometry, complex 5 is similar to the related trialkyl scandium complex with
6-dimethylamino-1,4-6-trimethyl-1,4-diazepine (L)Sc(CH2SiMe3)3 (1 in Chapter 2). There is
a noticeable difference in the bonding of the three amine donors for these two scandium
complexes: the Sc-N distance for the NMe2-group is intermediate between the other two
Sc-N distances in 1, whereas the Sc-N distance for the pyrrolidinyl-group is the longest of the
three Sc-N distances in 5. The coordination of L1 is to a large extent dictated by minimizing
the intramolecular interaction between the pyrrolidinyl group and the trimethylsilylmethyl
groups. This can also be seen by the significant difference in orientation of one of the alkyl
groups in 5 versus 1: the torsion angle of N(3)-Sc-C(17)-Si(2) in 5 is 100.51(13)˚ and the
corresponding torsion angle in 1 is -58.1(3)˚. For complex 6, the averaged Y-N distance
(2.625 Å) is slightly longer than that reported for (Me3[9]aneN3)Y(CH2SiMe3)311 (Y-N 2.601
Å; Y-C 2.427 Å), whereas the averaged Y-C bond lengths in the two compounds are very
similar (Y-C 2.429 Å for 6). Comparing the averaged M-N and M-C distances for 5 and 6
indicates that those for Sc are 0.13-0.14 Å shorter, corresponding to the difference in ionic
radius between Sc (0.75 Å) and Y (0.90 Å) for a coordination number of 6.12
Table 3.1. Selected Geometrical Data of Compounds 5 and 6.
5 6
Bond lengths (Å)
Sc-N(1) 2.4532(13) Y-N(1) 2.6419(16)
Sc-N(2) 2.5098(13) Y-N(2) 2.5647(16) Sc-N(3) 2.5270(12) Y-N(3) 2.6726(17)
Sc-C(13) 2.2699(16) Y-C(13) 2.388(2) Sc-C(17) 2.2735(16) Y-(C17) 2.444(2)
Sc-C(21) 2.2818(16) Y-C(21) 2.454(2) Bond angles (deg)
N(1)-Sc-C(21) 154.93(5) N(1)-Y-C(17) 150.40(6) N(2)-Sc-C(17) 159.61(5) N(2)-Y-C(21) 157.89(6)
N(3)-Sc-C(13) 160.48(5) N(3)-Y-C(13) 157.85(6)
3.2.2 Synthesis and Characterization of Tribenzyl Complexes (L1)M(CH2Ph)3 (M = Sc, La).
The rare earth tribenzyl compounds M(CH2Ph)3(THF)3 are convenient organo rare earth
metal starting materials that are readily accessible by reaction of metal trihalides MX3(THF)n
Chapter 3
38
with benzyl potassium.8 The tribenzyl complexes (L1)M(CH2Ph)3 (M = Sc, 7; M = La, 8)
were synthesized by reaction of M(CH2Ph)3(THF)3 (M = Sc, La) with L1 in THF (Scheme 3.2)
and were isolated as crystalline materials by crystallization from THF (isolated yields: 7,
80%; 8, 75%). Compounds 7 and 8 are rather poorly soluble in hydrocarbon solvents and
sparingly soluble in THF and C6H5Br. The 1H NMR resonances (in C6D5Br) for ligand L1 in
the compounds 7 and 8 are very similar to those in compounds 5 and 6. Solution NMR
spectroscopy of the Sc compound 7 in C6D5Br at ambient temperature showed two sets of
signals for three benzyl groups in a ratio of 1:2. The 1H NMR resonances of Sc-CH2 are
found at δ 2.60 and 2.41 ppm and the corresponding 13C NMR resonances at δ 61.6 and 60.7
ppm. This indicates that compound 7 is geometrically rigid in solution on the NMR time
scale. In contrast, NMR spectroscopy of the La compound 8 in C6D5Br at ambient
temperature showed that the three benzyl groups on lanthanum center are equivalent,
indicative of fluxionality of 8 in solution on the NMR time scale. The resonances of La-CH2
are found at δ 1.68 ppm (1H) and δ 69.2 ppm (13C). Once dissolved in THF-d8 ([La] = 10 mM),
compound 8 partially loses the ligand L1 and forms a mixture of La(CH2Ph)3(THF-d8)3 and 8
with Keq = 1.01 × 10-6 at 25 ˚C, as seen by the 1H NMR spectroscopy. This ligand
dissociation was not observed for the scandium compound 7 in THF-d8.
Scheme 3.2. Synthesis of the Tribenzyl Complexes 7 and 8.
Crystal structure determinations of 7 and 8 were performed and their structures are shown
in Figure 3.2, and the geometrical data are listed in Table 3.2. Compound 7, like compound 5,
features an approximately octahedral Sc center with the coordination sphere composed of
three nitrogen atoms of ligand L1 and three 1-bound benzyl ligands, with Sc-CH2-Cipso
angles of 115.7(13)-132.7(14). The three Sc-N distances (2.4292(19) Å, 2.4331(17) Å, and
Equation used to calculate the equilibrium constant Keq:
In a solution of (L)La(CH2Ph)3 (10 mM) in THF-d8, (L)La(CH2Ph)3 (6.5 mM), La(CH2Ph)3(THF-d8)
(3.5 mM), and L (3.5 mM) were detected by 1H NMR spectroscopy. [THF-d8] (12.3 M) was used to
calculate Keq.
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
39
2.4512(16) Å) in 7 are comparable, and noticeably shorter than those in 5 (2.4532(13) Å,
2.5098(13) Å, and 2.5270 Å). Unlike its precursor La(CH2Ph)3(THF)3 which has three
2-bound benzyl groups, 8 contains one 1-bound, one 2-bound, and one 3-bound benzyl
group with La-CH2-Cipso angles of 121.3(5), 96.6(4), and 87.7(4), respectively. The
3-bound benzyl has a phenyl group that is significantly tilted, with the difference of 0.61 Å
between two La-Co distances (La-C(33) = 3.177(8) Å and La-C(29) = 3.785(8)Å). Benzyl
groups 3-bound to a rare earth metal center have precedent e.g. in
[PhC(NAr)2]La(CH2Ph)2(THF) (Ar = 2,6-iPr2C6H3)8c and (C5Me5)2MCH2Ph (M = Sm13a and
Ce13b).
Figure 3.2. Molecular structure of 7 (left) and 8(right). Hydrogen atoms are omitted for clarity and thermal ellipsoids drawn at the 50% probability level.
Table 3.2. The geometrical data of compounds 7 and 8.
7 8
Bond lengths (Å)
Sc-N(1) 2.4292(19) La-N(1) 2.736(5) Sc-N(2) 2.4331(17) La-N(2) 2.816(6)
Sc-N(3) 2.4512(18) La-N(3) 2.775(5) Sc-C(13) 2.341(2) La-C(13) 2.716(7)
Sc-C(20) 2.314(2) La-C(20) 2.633(7) La-C(21) 3.154(7)
Sc-C(27) 2.295(2) La-C(27) 2.661(7) La-C(28) 2.965(7)
La-C(33) 3.177(8) Bond angles (deg)
Sc-C(13)-C(14) 115.72(17) La-C(13)-C(14) 121.3(5) Sc-C(20)-C(21) 125.21(14) La-C(20)-C(21) 96.6(4)
Sc-C(27)-C(28) 132.73(14) La-C(27)-C(28) 87.7(4)
Chapter 3
40
3.2.3 Reactions of L2 with Trialkyls M(CH2SiMe3)3(THF)2 (M = Sc, Y): Alkylation of the Imino Functionality by the M-Alkyl Bond.
Reaction of ligand L2 with the group 3 metal trialkyls M(CH2SiMe3)3(THF)2 (M = Sc
and Y) was rapid and quantitative in C6D6 as seen by 1H NMR spectroscopy. This resulted
in a product in which the imine carbon atom of the ligand has been alkylated to give the
tridentate monoanionic ligand {(Me3SiCH2)PhC(H)NCMe[(CH2NMeCH2)2]}- (L19)
(Scheme 3.3). Such intramolecular alkylation of ligand imino functionalities by M-alkyl
bonds has been observed previously for early transition metals.14 On a preparative scale,
these two complexes (L19)M(CH2SiMe3)2(THF)x (M = Sc, x = 0, 9; M = Y, x = 1, 10) were
obtained as colorless crystalline materials (isolated yields: 9, 84%; 10, 77%) by reaction of
M(CH2SiMe3)3(THF)2 with ligand L2 in toluene at room temperature, followed by removal
of all the volatiles and recrystallization from a toluene/n-hexane solution.
Scheme 3.3. Reaction of Ligand L2 with M(CH2SiMe3)3(THF)2.
The structures of complexes 9 and 10 were established by single-crystal X-ray diffraction
and are shown in Figure 3.3, with the geometrical data listed on Table 3.3. Each of these
two complexes contains two trimethylsilylmethyl ligands and a monoanionic fac-tridentate
ligand in which the nitrogen on the 6-position of the 1,4-diazepane skeleton is an amide
with a (Me3SiCH2)PhCH substituent. Different from the 5-coordinate scandium complex 9,
yttrium complex 10 is a 6-coordinate complex containing one THF molecule which is
located in a trans position relative to the amido nitrogen. The M-N(amido) distances of
2.0498(14) Å for 9 and 2.215(3) Å for 10 are substantially shorter than the corresponding
M-N(amino) distances to the remaining amine nitrogens in ligand L19.
The solution NMR spectra of 9 and 10 in toluene-d8 are consistent with the structures as
determined by X-ray diffraction. Low-temperature solution NMR studies on both
complexes reveal fully asymmetrical structures, as seen by two N-Me resonances (δ 2.06
and 1.97 ppm for 9; δ 2.15 and 2.11 ppm for 10), two Si-Me resonances (δ 0.63 and 0.47
ppm for 9; δ 0.58 and 0.54 ppm for 10) of the alkyl groups attached to the metal center, and
two resonances (δ 2.25 and 2.09 ppm for 9; δ 2.44 and 2.12 ppm for 10) for the
diastereotopic methylene protons of the alkyl group transferred to the ligand precursor L2.
For each complex, two sets of diastereotopic 1H resonances were observed for M-CH2
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
41
groups: MCH2 groups in 9 exhibit 1H resonances at δ 0.00 and -0.14 ppm (d, JHH = 11.2 Hz)
for one alkyl group and δ -0.02 and -0.10 ppm (d, JHH = 11.2 Hz) for the other; MCH2
groups in 10 exhibit 1H resonances at δ 0.18 and -0.88 ppm (d, JHH = 11.0 Hz) for one alkyl
group and δ -0.50 and -0.74 ppm (d, JHH = 11.5 Hz) for the other.
Figure 3.3. Molecular structures of complexes 9 (left) and 10 (right). Hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Table 3.3. Selected Geometrical Data of Compounds 9 and 10.
9 10
Bond lengths (Å)
Sc-N(1) 2.3432(13) Y(1)-N(11) 2.695(3)
Sc-N(2) 2.4911(15) Y(1)-N(12) 2.598(3) Sc-N(3) 2.0498(14) Y(1)-N(13) 2.215(3)
Sc-C(20) 2.2733(17) Y(1)-C(120) 2.469(3) Sc-C(24) 2.2730(17) Y(1)-(C124) 2.446(4)
Y(1)-O(1) 2.487(3) Bond angles (deg)
N(1)-Sc-N(2) 68.48(5) N(11)-Y(1)-N(12) 62.94(10) N(2)-Sc-N(3) 73.99(5) N(12)-Y(1)-N(13) 71.39(11)
N(1)-Sc-N(3) 84.32(5) N(11)-Y(1)-N(13) 74.85(10) N(1)-Sc-C(24) 129.42(6) N(11)-Y(1)-C(120) 157.45(10)
N(2)-Sc-C(20) 162.56(6) N(12)-Y(1)-C(124) 151.54(14) C(20)-Sc-C(24) 101.97(6) N(13)-Y(1)-O(1) 152.12(10)
To see whether the imino group in ligand HL5 (with a phenolic substituent on the aldimine
carbon) can be alkylated by the Y-alkyl bond, reaction of HL5 with Y(CH2SiMe3)3(THF)2
was performed. This afforded a product (11, Scheme 3.4) in which the phenolic –OH group
of the ligand has been deprotonated, and where the imino ligand moiety remains intact (as
Chapter 3
42
evidenced by the 1H and 13C NMR resonances at 7.64 ppm and 161.1 ppm for the
aldimine –CH=N group and the C=N IR band at 1622 cm-1). It was obtained (isolated yield:
78%) as an off-white crystalline material. Although suitable crystals of 11 for a single crystal
structure determination have not yet been obtained, the solution 1H and 13C spectra indicate a
Cs symmetric structure with a tetradentate iminophenolate diazepane ligand and two alkyl
groups attached to the metal centre. The yttrium is 6-coordinate, as no additional THF is
bound. The NMR resonances for the YCH2 groups are found at -0.51 and -0.55 ppm (1H; 2JHH = 11.3 Hz, 1JYH = 2.9 Hz) and 30.0 ppm (13C; 1JYC = 38 Hz). The compound is related
to the triazacyclononane-phenolate complex of scandium reported by Mountford et al.15
Scheme 3.4. Synthesis of Yttrium Dialkyl Complex 11.
Scheme 3.5. Generation of the Ionic Complexes 12 and 13.
3.3 Synthesis of Cationic Organo Rare Earth Metal Complexes with
Neutral Ligand L1
Upon reaction of the trialkyl complexes 5 and 6 with one equiv of [PhNMe2H][B(C6F5)4]
in the weakly coordinating solvent C6D5Br, instantaneous liberation of 3 equiv of TMS was
observed by 1H NMR spectroscopy and no well-defined cations could be identified.
Apparently, the initially formed dialkyl cation is thermally labile, decomposing through
ligand H-abstraction processes. This decomposition of the dialkyl cations can be prevented
when the reactions are carried out in THF (Scheme 3.5). When the tetraphenylborate salt
[PhNMe2H][B(C6H5)4] was used as reagent, the ionic compounds
[(L1)M(CH2SiMe3)2(THF)][B(C6H5)4] (M = Sc, 12; M = Y, 13) could be isolated as
analytically pure white microcrystalline powders by layering their THF solutions with
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
43
n-hexane (isolated yield: 12, 84%; 13, 86%). The compounds contain one THF molecule per
metal center, as seen by elemental analysis.
The structure of 12 was established by single crystal X-ray diffraction and is shown in
Figure 3.4 (the geometrical data of 12 are listed in Table 3.4 together with those of its neutral
precursor 5, with geometrically related parameters juxtaposed for easy comparison). The
geometry around the scandium center in the cation of 12 is again distorted octahedral, as in its
neutral trialkyl precursor 5. The ligand in 12 is bound more tightly to the Sc center than in 5,
as seen by the shorter Sc-N average distance (2.432 Å) and the larger N-Sc-N average angle
(72.71˚) in 12 compared with those in 5 (av. Sc-N = 2.4967 Å; av. N-Sc-N = 69.89˚),
indicating that the Sc center in the cation of 12 is more electrophilic. The differences between
the corresponding Sc-C and Sc-N distances in neutral and cationic species are relatively
small, with one notable exception. The position taken in the neutral compound 5 by the alkyl
group trans to the pyrrolidinyl nitrogen, with the shortest Sc-C(13) distance (2.2699 Å) and
largest N(3)-Sc-C(13) angle (160.48˚), is occupied in the ionic compound 12 by the
coordinated THF molecule. With this, the longest Sc-N (2.527 Å) bond (to the pyrrolidinyl
nitrogen N(3)) in 5 becomes the shortest Sc(1)-N(13) (2.396 Å) bond with N(13)-Sc(1)-O(11)
= 160.63˚ in 12, indicating that the Sc-N(amine) distances in these complexes are very
sensitive to the nature of the group trans to it. Similar phenomena were observed previously
in various triamine-amide rare earth metal alkyl complexes.16
Figure 3.4. Molecular structure of 12. Hydrogen atoms and the anion [B(C6H5)4]- are
omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
In contrast to the trialkyl complexes 5 and 6, the tribenzyl compounds 7 and 8 can be
cleanly converted to the corresponding cations [(L1)M(CH2Ph)2]+ by reaction with
[PhNMe2H][B(C6F5)4] in C6D5Br (as seen by NMR spectroscopy), accompanied by release
of toluene and free PhNMe2. Both cations are thermally robust and can be stored in C6D5Br
Chapter 3
44
solution for at least one day without decomposition. This enhanced thermal stability in the
absence of THF might be due to multihapto coordination of the remaining benzyl groups.
The 13C NMR resonances of the M-CH2Ph groups are found at δ 64.7 ppm for
[(L1)Sc(CH2Ph)2]+ and δ 71.7 ppm for [(L1)La(CH2Ph)2]
+, showing a typical downfield shift
compared with their neutral precursors (61.1 ppm for 7 and 69.2 ppm for 8), associated with
generation of cationic species.2c,2h
Table 3.4. The Geometrical Data of Complexs 12 and 5.
12 5
Bond lengths (Å)
Sc(1)-N(11) 2.441(4) Sc-N(2) 2.5098(13) Sc(1)-N(12) 2.460(5) Sc-N(1) 2.4532(13)
Sc(1)-N(13) 2.396(5) Sc-N(3) 2.5270(12) Sc(1)-C(113) 2.236(5) Sc-C(21) 2.2818(16)
Sc(1)-C(117) 2.289(6) Sc-C(17) 2.2735(16) Sc(1)-O(11) 2.219(4) Sc-C(13) 2.2699(16)
Bond angles (deg) N(11)-Sc(1)-N(12) 67.11(15) N(1)-Sc-N(2) 66.46(4)
N(11)-Sc(1)-N(13) 73.73(14) N(2)-Sc-N(3) 69.88(4) N(12)-Sc(1)-N(13) 77.29(15) N(1)-Sc-N(3) 73.33(4)
N(11)-Sc(1)-C(117) 158.07(16) N(1)-Sc-C(21) 154.93(5) N(12)-Sc(1)-C(113) 168.37(18) N(2)-Sc-C(17) 159.61(5)
N(13)-Sc(1)-O(11) 160.63(14) N(3)-Sc-C(13) 160.48(5)
Scheme 3.6 General Catalytic Cycle for Intramolecular Hydroamination/cyclization.
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
45
3.4 Comparative catalysis study of intramolecular hydroamination
cyclization of aminoalkenes
The intramolecular hydroamination/cyclization of aminoalkenes by organo rare earth
metal catalysts has been extensively investigated.4 Nevertheless, only a limited number of
reports exist concerning the comparative study of neutral catalysts vs their cationic
congeners.8c,17 In this contribution, we have compared the activities of the neutral and
cationic rare earth metal alkyl or benzyl complexes supported by L1 in the catalytic
intramolecular hydroamination/cyclization reaction of 2,2-diphenylpent-4-en-1-amine (S1)
and N-methylpent-4-en-1-amine (S2). Control experiments with Sc(CH2Ph)3(THF)3,
Y(CH2SiMe3)3(THF)3, La(CH2Ph)3(THF)3, and their monocationic derivatives were also
carried out. All cationic species were generated in situ from neutral precursors by reaction
with [PhNMe2H][B(C6F5)4].
Table 3.5. Catalytic Hydroamination/Cyclization of 2,2-diphenyl-4-pentenylamine (S1).
Entry Catalyst Time / (min) Conv. / (%)c k / l.mol-1.s-1
1 Sc(CH2Ph)3(THF)3 600b 40 4.74 × 10-4
2 5 or 7 600b 54 9.00 × 10-4
3 Sc(CH2Ph)3(THF)3/B 500b >99 5.34 × 10-3
4 5 or 7/B 240b 0
5 Y(CH2SiMe3)3(THF)3 600b >99 3.68 × 10-3
6 6 400b >99 7.48 × 10-3
7 Y(CH2SiMe3)3(THF)2/B 180 88 d
8 6/B 5 >99 8.11 × 10-1
9 La(CH2Ph)3(THF)3 200 >99 1.98 × 10-2
10 8 200 >99 1.99 × 10-2
11 La(CH2Ph)3(THF)3/B 240 51 d
12 8/B 70 >99 6.48 × 10-2 a Conditions: C6D6 solvent (total volume 0.5 ml), 60 ˚C, catalyst (10 μmol) and activator
[PhNMe2H][B(C6F5)4] (B, 10 μmol) where appropriate, substrate (500 μmol); b 80 ˚C; c
Determined by in-situ NMR spectroscopy; d Not determined, due to the poor solubility of
the catalyst.
For substrate S1 (Table 3.5), a comparison of the neutral and cationic catalyst species shows that for both types of species the reactions are first order in substrate
concentration over the full conversion range. Most catalyzed cyclizations of S1 and related substrates show a zero order dependence on substrate concentration, consistent
Chapter 3
46
with rate-determining intramolecular insertion of the olefin into the metal-nitrogen
bond (Scheme 3.6).4j-l Deviations from this behavior are often found at higher substrate conversions, where they are associated with product inhibition (formation of metal
secondary amide species).4g,h,j,k We observed a few instances of first order behavior over the full conversion range with non-metallocene rare earth metal catalysts before,9
but as yet have no unambiguous explanation for this phenomenon. For neutral catalysts
5-8, compound 8, with the largest metal (La), shows the highest activity (entries 2, 6, and 10). No catalytic activity was observed for the cationic Sc system (entry 4) and the cationic Y and La species show higher activities than their neutral precursors (entries 6
and 8; 10 and 12). Remarkably, the activity of the Y catalyst increases substantially when converted to the cationic species (entry 6 and 8), producing easily the most active
catalyst in the entire series. The control experiments (entries 1, 5, and 9) indicate that
the neutral ligand L1 does enhance the activity (except for the neutral La system),
especially for the cationic systems where the catalysts are sparingly soluble without L1 and precipitate as oily materials during the catalysis. For the neutral La system, 8 and
La(CH2Ph)3(THF)3 show the same activity, indicating L1 may dissociate from the metal in the presence of excess amine S1. This is plausible, considering our observation (in
section 3.2.2) that dissociation of L1 occurs when 8 is dissolved in neat THF.
Table 3.6. Catalytic Hydroamination/Cyclization of 2,2-diphenyl-4-pentenylamine (S2).
Entry Catalyst Time / (min) Conv. / (%)b k / s-1 c
1 Sc(CH2Ph)3(THF)3 30 >99 1.10×10-1 mol-1.L.s-1
2 5 30 >99 9.88×10-2 mol-1.L.s-1
3 Sc(CH2Ph)3(THF)3/B 240 72 4.50×10-3 mol-1.L.s-1
4 5/B 240 0
5 Y(CH2SiMe3)3(THF)2 25 >99 4.18×10-2
6 6 40 >99 4.12×10-2
7 Y(CH2SiMe3)3(THF)2/B 40 >99 2.58×10-2
8 6/B 275 >99 4.50×10-3
9 La(CH2Ph)3(THF)3 15 >99 9.15×10-2
10 8 15 >99 1.00×10-1
11 La(CH2Ph)3(THF)3/B 10 >99 1.31×10-1
12 8/B 10 >99 1.32×10-1
a Conditions: C6D6 solvent (total volume 0.5 ml), 60 ˚C, catalyst (10 μmol) and activator
[PhNMe2H][B(C6F5)4] (B, 10 μmol) where appropriate, substrate (500 μmol); b Determined
by in-situ NMR spectroscopy; c Calculated over the first 50% conversion.
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
47
Another substrate employed in this study is a secondary amine S2 and the results are
summarized in Table 3.6. All the reactions essentially go to completion (except for 5/B) and
the catalysts with the metal with the largest ionic radius (La) show higher activity. The
catalysis by Y and La systems show a zero order dependence in substrate concentration over
the first 50% conversion (characteristic of rate limiting intramolecular alkene insertion into
the metal-amido bond; Scheme 3.6), indicating a change in rate determining step at lower
substrate concentrations. In contrast, a first order dependence on the substrate concentration
was observed for the Sc catalysts. For Sc catalysts, 5 and Sc(CH2Ph)3(THF)3 show similar
reaction rates (entry 1 and 2) and no conversion was observed for the cationic system 5/B.
For the Y catalysts, the cationic species in this case is less active than its neutral precursor
(entries 6 and 8), but the cationic system is more active for the La systems (entries 10 and 12).
The control experiments indicated that L1 actually slows down the catalysis by the Y
catalysts (entries 5 and 6; 7 and 8). This might be due to the increased steric demand of the
secondary amine substrate S2 relative to S1 and relatively strong coordination of the ligand
to the Y center during the catalysis, thus making the Y center sterically more crowded. This
can also be seen by the observation that all alkyl groups of Y(CH2SiMe3)3(THF)2 were
instantaneously protonated upon mixing with S2 whereas some of the alkyl groups attached
to the Y center in 6 were still detectable (by 1H NMR spectroscopy) even after 20 min at 60
˚C during the catalysis. For the larger metal La, L1 does not influence the catalysis by either
neutral or cationic catalysts.
3.5 Concluding Remarks
We have shown that the 1,4,6-trimethyl-6-pyrrolidin-1-yl-1,4-diazepane ligand (L1) is
suitable to support well-defined neutral and cationic trimethylsilylmethyl and benzyl
scandium, yttrium, and lanthanum complexes, and can thus be applied over the full size range
of the rare earth metals. The benzyl group imparts greater stability to these complexes than
the trimethylsilylmethyl group. This is likely to be due to the possibility of multi-hapto
bonding of the benzyl groups, illustrated e.g. by the structure of (L1)La(CH2Ph)3 (8) that
contains one η1, one η2 and one η3 group. Whereas the tridentate ligand L1 is apparently
tightly bound to Sc and Y, it is readily displaced from the large La-center by a large excess of
monodentate Lewis bases. The imino group of the neutral ligand L2 is susceptible to
alkylation by the M-alkyl bond upon reaction with the group 3 metal trialkyls, thus
converting the neutral ligand L2 to the monoanionic 1,4-diazepan-6-amido ligand L19. No
such alkylation was observed for the imino group in the monoanionic tetradentate N3O ligand
L5.
The prepared neutral compounds and their monocationic derivatives catalyze the
intramolecular hydroamination/cyclization of primary and secondary aminoalkenes. The
substrates display quite different requirements for effective catalysis: the primary amine
2,2-diphenylpent-4-en-1-amine is most efficiently converted by the cationic (L1)Y-catalyst,
Chapter 3
48
but the secondary amine N-methylpent-4-en-1-amine simply prefers the least sterically
encumbered catalyst (the cationic La system).
3.6 Experimental Section
General Remarks. See the corresponding section in Chapter 2. M(CH2SiMe3)3(THF)2 (M
= Sc and Y)10, Sc(CH2Ph)3(THF)3,8a La(CH2Ph)3(THF)3
8c, 2,2-diphenyl-4-pentenylamine18a,
and N-methyl-4-pentenylamine18b were prepared according to published procedures.
Synthesis of (L1)Sc(CH2SiMe3)3 (5). To a solution of Sc(CH2SiMe3)3(THF)2 (0.44 g, 0.98
mmol) in toluene (20 mL), was added dropwise a solution of L1 (0.21 g, 0.99 mmol) in
toluene (20 mL) while stirring. The mixture was stirred at room temperature for 30 min and
then the volatiles were removed under reduced pressure. The slightly yellow residue was
dissolved in toluene (3 mL) and pentane (5 mL) was layered on top. Upon cooling to -30 °C,
crystalline material formed, including material suitable for X-ray diffraction. The mother
liquor was decanted and the solid was dried under reduced pressure yielding the title
compound (0.37 g, 0.71 mmol, 72%) as a slightly yellow solid. 1H NMR (400 MHz, C6D6) δ:
3.10 (m, 2H, Py α-H), 3.08 (m, 2H, NCH2), 2.25 (d, 2H, JHH = 14.0 Hz, CCH2), 2.19 (s, 6H,
NCH3), 2.02 (m, 2H, Py α-H), 1.76 (m, 2H, Py β-H), 1.54 (m, 2H, NCH2), 1.35 (d, 2H, JHH =
14.0 Hz, CCH2), 1.31 (m, 2H, Py β-H), 0.47 (s, 27H, Si(CH3)3), -0.0 (s, 3H, CCH3), -0.11 (br,
6H, ScCH2). 13C NMR (100.6 MHz, C6D6) δ: 70.5 (t, JCH = 138.1 Hz, CCH2), 59.5 (s, CCH3),
59.1 (t, JCH = 138.4 Hz, NCH2), 50.8 (q, JCH = 136.6 Hz, NCH3), 48.1 (t, JCH = 134.8 Hz, Py
α-C), 39.7 (br, ScCH2, the JCH coupling on ScCH2 is not resolved), 24.5 (t, JCH = 131.3 Hz, Py
β-C), 12.2 (q, JCH = 127.3 Hz, CCH3), 4.7 (q, JCH = 117.0 Hz, Si(CH3)3). Anal. Calc for
C24H58N3Si3Sc: C, 55.65; H, 11.29; N, 8.11. Found: C, 55.48; H, 11.26; N, 7.81.
Synthesis of (L1)Y(CH2SiMe3)3 (6). It was prepared according the procedure described
for 5. Y(CH2SiMe3)3(THF)2 (0.49 g, 99.0 μmol) and L1 (0.21 g, 99.4 μmol) were used as
starting materials and the title compound was obtained as a white solid. Yield: 0.34 g, (60.5
μmol, 61%). 1H NMR (400 MHz, C6D6) δ: 3.07 (m, 2H, NCH2), 3.06 (m, 2H, Py α-H), 2.17
(d, 2H, JHH = 14.3 Hz, CCH2), 2.16 (s, 6H, NCH3), 2.03 (m, 2H, Py α-H), 1.75 (m, 2H, Py
β-H), 1.53 (m, 2H, NCH2), 1.32 (m, 2H, Py β-H), 1.31 (d, 2H, JHH = 14.3 Hz, CCH2), 0.47 (s,
27H, Si(CH3)3), -0.03 (s, 3H, CCH3), -0.54 (d, 6H, JHH = 2.8 Hz, YCH2). 13C NMR (100.6
MHz, C6D6) δ: 69.9 (t, JCH = 135.1 Hz, CCH2), 59.7 (s, CCH3), 58.2 (t, JCH = 138.3 Hz,
NCH2), 49.7 (q, JCH = 136.0 Hz, NCH3), 47.0 (t, JCH = 138.3 Hz, Py α-C), 35.5 (dt, JCH = 96.5
Hz, JYC = 36.2 Hz, YCH2), 24.6 (t, JCH = 134.3 Hz, Py β-C), 12.2 (q, JCH = 129.0 Hz, CCH3),
4.9 (q, JCH = 115.8 Hz, Si(CH3)3). Anal. Calc (C24H58N3Si3Y): C, 51.3; H, 10.40; 7.48. Found:
C, 51.0; H, 10.42; N, 7.46.
Synthesis of (L1)Sc(CH2Ph)3 (7). To a solution of Sc(CH2Ph)3(THF)3 (0.242 g, 0.453
mmol) in THF (10 mL), was added a solution of L1 (0.096 g, 0.454 mmol) in THF (10 mL).
The resulting mixture was stirred at room temperature for 30 min and then concentrated to 4
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
49
ml. Upon cooling to -30 °C, colorless crystalline material formed. The mother liquor was
decanted and the solid was dried under vacuum, yielding the title compound
(L)Sc(CH2Ph)3.(THF) (0.217 g, 0.361 mmol, 80%) as colorless crystals. Crystals suitable for
X-ray analysis were grown from a saturated THF solution. 1H NMR (500 MHz, C6D5Br) δ:
7.15 (t, 4H, JHH = 7.43 Hz, m-H Ph), 7.07 (t, 2H, JHH = 7.47 Hz, m-H Ph), 7.04 (d, 4H, JHH =
7.54 Hz, o-H Ph), 6.89 (d, 4H, JHH = 7.58 Hz, o-H Ph), 6.74 (t, 2H, JHH = 7.24 Hz, p-H Ph),
6.68 (t, 1H, JHH = 7.11 Hz, p-H Ph), 2.99 (m, 2H, Py α-H), 2.74 (m, 2H, NCH2), 2.60 (br, 2H,
ScCH2), 2.41 (br, 4H, ScCH2), 2.41 (d, 2H, JHH = 14.0 Hz, CCH2), 2.03 (s, 6H, NCH3), 1.97
(m, 2H, Py α-H), 1.74 (m, 2H, Py β-H), 1.67 (m, 2H, NCH2), 1.63 (d, 2H, JHH = 14.0 Hz,
CCH2), 1.33 (m, 2H, Py β-H), 0.26 (s, 3H, CCH3). {1H}13C NMR (125.7 MHz, C6D5Br) δ:
154.4 (ipso-C Ph), 154.1 (ipso-C Ph), 128.0 (m-C Ph), 127.9 (m-C Ph), 124.3 (o-C Ph), 123.5
(o-C Ph), 117.5 (p-C Ph), 117.4 (p-C Ph), 70.8 (CCH2), 61.6 (br, ScCH2), 60.7 (br, ScCH2),
59.6 (CCH3), 58.1 (NCH2), 49.7 (NCH3), 47.5 (Py α-C), 24.7 (Py β-C), 11.9 (CCH3). Anal.
Calcd for C37H54N3OSc: C, 73.84; H, 9.04; N, 6.98. Found: C, 73.31; H, 8.93; N, 6.96.
Synthesis of (L1)La(CH2Ph)3 (8). It was prepared according the procedure described for 7.
La(CH2Ph)3(THF)3 (233.8 mg, 0.372 mmol) and L1 (78.6 mg, 0.372 mmol) were used as
starting materials and the title compound was obtained as a yellow crystalline solid. Yield:
172.6 mg, (0.278 mmol, 75%). 1H NMR (500 MHz, C6D5Br) δ: 7.11 (t, 6H, JHH = 7.83 Hz,
m-H Ph), 6.62 (t, 3H, JHH = 7.25 Hz, p-H Ph), 6.60 (d, 6H, JHH = 7.47 Hz, o-H Ph), 2.74 (m,
2H, NCH2), 2.60 (m, 2H, Py α-H), 2.36 (d, 2H, JHH = 14.3 Hz, CCH2), 2.04 (s, 6H, NCH3),
2.04 (m, 2H, Py α-H), 1.74 (m, 2H, NCH2), 1.69 (d, 2H, JHH = 14.3 Hz, CCH2), 1.68 (s, 6H,
LaCH2), 1.58 (m, 2H, Py β-H), 1.37 (m, 2H, Py β-H), 0.28 (s, 3H, CCH3). {1H}13C NMR
(125.7 MHz, C6D5Br) δ: 151.8 (ipso-C Ph), 129.7 (m-C Ph), 121.8 (o-C Ph), 116.0 (p-C Ph),
69.6 (CCH2), 69.2 (LaCH2), 60.5 (CCH3), 57.0 (NCH2), 48.7 (NCH3), 45.7 (Py α-C), 25.8
(Py β-C), 12.5 (CCH3). Anal. Calcd for C33H46N3La: C, 63.55; H, 7.43; N, 6.74. Found: C,
62.82; H, 7.41; N, 6.56.
Reaction of L2 with Sc(CH2SiMe3)3(THF)2: synthesis of (L19)Sc(CH2SiMe3)2 (9). To a
solution of Sc(CH2SiMe3)3(THF)2 (0.239 g, 0.53 mmol) in toluene (10 mL), was added a
solution of L2 (0.13 g, 0.53 mmol) in toluene (10 mL) and the resulting solution was stirred at
room temperature for 30 min. All the volatiles were removed under reduced pressure and the
residue was purified by crystallization from a toluene/n-hexane mixture, yielding the title
compound (0.226 g, 0.41 mmol, 77%) as an off-white solid. 1H NMR (500 MHz, toluene-d8,
-50 ˚C) δ: 4.03 (dd, 1H, JHH = 12.3 Hz, JHH = 3.4 Hz, PhCH), 2.43 (m, 1H, NCHH), 2.27 (d,
1H, JHH = 12.4 Hz, CCHH), 2.25 (m, 1H, JHH not resolved due to overlap, Me3SiCHH), 2.12
(d, 1H, JHH = 11.7 Hz, CCHH), 2.11 (m, 1H, NCHH), 2.09 (m, 1H, JHH not resolved due to
overlap, Me3SiCHH), 2.06 (s, 3H, NCH3), 1.97 (s, 3H, NCH3), 1.47 (m, 1H, NCHH), 1.45 (d,
1H, JHH = 12.4 Hz, CCHH), 1.36 (m, 1H, NCHH), 1.27 (d, 1H, JHH = 11.7 Hz, CCHH), 0.63
(s, 9H, Si(CH3)3), 0.47 (s, 9H, Si(CH3)3), 0.30 (s, 3H, CCH3), 0.15 (d, 1H, JHH = 11.2 Hz,
ScCHH), 0.00 ((d, 1H, JHH = 11.2 Hz, ScCHH), -0.02 (s, 9H, Si(CH3)3), -0.10 (d, 1H, JHH =
Chapter 3
50
11.2 Hz, ScCHH), -0.14 (d, 1H, JHH = 11.2 Hz, ScCHH). 13C{1H} NMR (125,7 MHz,
toluene-d8, -50 ˚C) δ: 152.8 (ipso-C Ph), 76.4 (CCH2), 71.2 (CCH2), 59.9 (PhCH), 57.6
(NCH2), 55.2 (CCH3), 55.0 (NCH2), 51.0 (NCH3), 50.5 (NCH3), 32.3 (ScCH2), 31.8 (ScCH2),
30.0 (Me3SiCH2CH), 21.7 (CCH3), 4.97 (Si(CH3)3), 4.90 (Si(CH3)3), -0.9 (Si(CH3)3). Anal.
Calcd for C27H56N3ScSi3: C, 58.85; H, 10.24; N, 7.63. Found: C, 59.50; H, 10.15; N, 7.28.
Reaction of L2 with Y(CH2SiMe3)3(THF)2: synthesis of (L19)Y(CH2SiMe3)2(THF) (10).
It was prepared according to the procedure described for 9. Y(CH2SiMe3)3(THF)2 (0.495 g,
1.0 mmol) and L2 (0.245 g, 1.0 mmol) were used as starting material and the title compound
(10.0.25(C7H8)) was obtained as a slightly yellow solid after crystallization from a
toluene/pentane mixture. Yield: 0.58g, (0.84mmol, 84%). 1H NMR (500MHz, C7D8, -60°C)
δ: Proton signals on the phenyl group are broad and overlap with solvent C7D8 signals. 4.56
(d, 1H, JHH = 12.5 Hz, PhCH), 3.53 (broad s, 2H, α-H THF), 3.41 (broad s, 2H, α-H THF),
2.72 (d, 1H, JHH = 11.0 Hz, NCHH), 2.44 (d, 1H, JHH = 11.9 Hz, SiCHH), 2.32 (d, 1H, JHH =
11.0 Hz, NCHH), 2.15 (s, 3H, NCH3), 2.12 (d, 1H, SiCHH, overlap with 2.11 ppm NCH3),
2.11 (s, 3H, NCH3), 2.03 (m, 2H, NCH2), 1.66 (d, 1H, JHH = 11.0 Hz, NCHH), 1.57 (d, 1H,
JHH = 11.0 Hz, NCHH), 1.48 (m, 2H, NCH2), 1.34 (broad s, 4H, β-H THF), 0.68 (s, 3H,
CCH3), 0.54 (s, 9H, Si(CH3)3), 0.58 (s, 9H, Si(CH3)3), 0.18 (s, 9H, Si(CH3)3), 0.18 (d, 1H,
YCHH, overlap with 0.18 ppm singlet), -0.50 (d, 1H, JHH = 11.5 Hz, YCHH), -0.74 (d, 1H,
JHH = 11.5 Hz, YCHH), -0.88 (d, 1H, JHH = 11.0 Hz, YCHH). The JYH coupling on the YCH2
protons is unresolved. 13C{1H} NMR (125.7MHz, C6D6, -60°C) δ: 155.4 (ipso-C Ph), 129.2
(o-C Ph), 128.3 (m-C Ph), 125.9 (p-C Ph), 81.0 ( NCH2), 77.1 (NCH2), 69.8 (α-C THF), 60.9
(PhCH), 57.2 (NCH2), 56.9 (CCH3), 50.0 (NCH3), 31.3 (d, JYC = 33.4 Hz, YCH2), 29.7
(SiCH2), 25.8 (d, JYC = 38.5 Hz, YCH2), 24.3 (β-C THF), 20.5 (CCH3), 4.67 (Si(CH3)3), 4.69
(Si(CH3)3), -0.82 (Si(CH3)3). Resonances for the (proteo)toluene in the crystals omitted.
Anal. Calcd for 2(C31H64N3OSi3Y).0.5(C7H8): C, 56.92; H, 9.63; N, 6.08. Found: C, 56.85; H,
9.58; N, 6.12.
Synthesis of (L5)Y(CH2SiMe3)2 (11). A solution of HL5 (0.261 g, 1.0 mmol) in cold
toluene (6 mL) was added to s solution of Y(CH2SiMe3)3(THF)2 (0.495 g, 1.0 mmol) in cold
toluene (20 mL). The mixture was allowed to warm to room temperature and stirred for 30
min. The volatiles were removed under reduced pressure and the residue was washed with
pentane yielding the title compound (L5)Y(CH2SiMe3)2 (0.41 g, 0.78 mmol, 78%) as an
off-white solid. 1H NMR (500MHz, C6D6) δ: 7.64 (s, 1H, N=CH), 7.29 (t, 1H, JHH = 7.26 Hz,
Ph), 7.23 (d, 1H, JHH = 7.75 Hz, Ph), 7.12 (d, 1H, JHH = 7.75 Hz, Ph), 6.67 (t, 1H, JHH = 7.26
Hz, Ph), 2.87 (m, 2H, NCH2), 2.02 (s, 6H, NCH3), 1.78 (d, 2H, JHH = 13.3 Hz, CCH2), 1.55
(m, 2H, NCH2), 1.53 (d, 2H, JHH = 13.3 Hz, CCH2), 0.42 (s, 18H, Si(CH3)3), 0.33 (s, 3H, C),
-0.51 (dd, 2H, JYH = 2.9 Hz, JHH = 11.3 Hz), -0.55 (dd, 2H, JYH = 2.9 Hz, JHH = 11.3 Hz), 13C{1H} NMR (125.7MHz, C6D6) δ: 166.6 (O-Ph), 161.1 (N=CH), 135.5 (Ph), 134.7 (Ph),
122.6 (Ph), 122.6 (Ph), 115.7 (Ph), 71.5 (CCH2), 62.1 (CMe), 57.2 (NCH2CH2), 49.4 (NMe2),
30.3 (d, YCH2, JYC = 38.2 Hz), 17.1 (CMe), 4.7 (SiMe3). Anal. Calcd for C23H44N3OSi2Y: C,
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
51
52.75%; H, 8.47%; N, 8.02%. Found: C, 52.83%; H, 8.43%; N, 8.03%.
Synthesis of [(L1)Sc(CH2SiMe3)2(THF)][B(C6H5)4] (12). THF (2 mL) was added to a
mixture of 5 (77.7 mg, 150 μmol) and [PhMe2NH][B(C6H5)4] (66.2 mg, 150 μmol). The
solution was homogenized by agitation and allowed to stand for about 20 min. n-Hexane (2
mL) was added to the mixture to form white precipitate and more THF was added to just
dissolve this precipitate. Colorless crystalline material formed upon cooling to -30 °C. The
mother liquor was decanted and the solid was dried under reduced pressure, yielding the title
compound (103.9 mg, 126 μmol, 84%) as a white solid. Crystals for single crystal X-ray
diffraction were obtained by recrystallization from a mixture of THF and toluene. 1H NMR
(500 MHz, THF-d8) δ: 7.32 (br, 8H, o-H Ph), 6.91 (t, 8H, JHH = 7.62 Hz, m-H Ph), 6.78 (t, 4H,
JHH = 7.35 Hz, p-H Ph), 3.62 (m, 4H, α-H THF), 3.36 (m, 2H, Py α-H), 2.93 (d, 2H, JHH =
14.3 Hz, CCH2), 2.75 (m, 2H, NCH2), 2.70 (m, 2H, Py α-H), 2.37 (s, 6H, NCH3), 2.26 (m, 2H,
NCH2), 2.23 (d, 2H, JHH = 14.3 Hz, CCH2), 2.04 (m, 2H, Py β-H) 1.87 (m, 2H, Py β-H), 1.77
(m, 4H, β-H THF), 0.69 (s, 3H, CCH3), -0.02 (s, 18H, Si(CH3)3), -0.27 (s, 4H, ScCH2). 13C
NMR (125.7 MHz, THF-d8) δ: 166.4 (q, JBC = 46.5 Hz, ipso-C Ph), 138.4 (d, JCH = 155.9 Hz,
o-C Ph), 127.1 (d, JCH = 152.7 Hz, m-C Ph), 123.3 (d, JCH = 159.1 Hz, p-C Ph), 71.6 (t, JCH =
138.3 Hz, CCH2), 69.4 (t, JCH = 134.6 Hz, α-C THF), 63.2 (s, CCH3), 60.2 (t, JCH = 139.4 Hz,
NCH2), 52.4 (q, JCH = 138.1 Hz, NCH3), 50.5 (t, JCH = 139.6 Hz, Py α-C), 47.6 (t, JCH = 94.6
Hz, ScCH2), 27.6 (t, JCH =132.2 Hz, β-C THF), 26.6 (t, JCH = 130.9 Hz, Py β-C), 14.4 (q, JCH
= 116.2 Hz, CCH3), 4.8 (q, JCH = 116.9 Hz, Si(CH3)3). Anal. Calcd for C48H75BN3OScSi2: C,
70.13; H, 9.20; N, 5.11. Found: C, 70.50; H, 9.22; N, 5.15.
Synthesis of [(L1)Y(CH2SiMe3)2(THF)][B(C6H5)4] (13). It was prepared according to the
procedure described for 12. Complex 6 (84.3 mg, 150 μmol) and [PhMe2NH][B(C6H5)4]
(66.2 mg, 150 μmol) were used as starting material. The title complex was obtained as a
white solid after crystallization from a THF/n-hexane mixture. Yield: 112 mg, (129 μmol,
86%). 1H NMR (500 MHz, THF-d8) δ: 7.32 (br, 8H, o-H Ph), 6.91 (t, 8H, JHH = 7.62 Hz, m-H
Ph), 6.78 (t, 4H, JHH = 7.35 Hz, p-H Ph), 3.61 (m, 4H, α-H THF), 3.19 (m, 2H, Py α-H), 2.94
(d, 2H, JHH = 14.4 Hz, CCH2), 2.86 (m, 2H, NCH2), 2.72 (m, 2H, Py α-H), 2.43 (s, 6H, NCH3),
2.35 (m, 2H, NCH2), 2.32 (d, 2H, JHH = 14.4 Hz, CCH2), 1.97 (m, 2H, Py β-H) 1.90 (m, 2H,
Py β-H), 1.77 (m, 4H, β-H THF), 0.72 (s, 3H, CCH3), -0.04 (s, 18H, Si(CH3)3), -0.74 (d, 4H,
JHH = 3.1 Hz, YCH2). 13C{1H} NMR (125.7 MHz, THF-d8) δ: 166.4 (q, JBC = 46.5 Hz, ipso-C
Ph), 138.4 (o-C Ph), 127.1 (m-C Ph), 123.3 (p-C Ph), 71.0 (CCH2), 69.4 (α-C THF), 63.1
(CCH3), 59.4 (NCH2), 51.2 (Py α-C), 48.8 (NCH3), 40.7 (d, JYC = 42.0 Hz, YCH2), 27.6 (β-C
THF), 26.5 (Py β-C), 14.3 (CCH3), 5.2 (Si(CH3)3). Anal. Calcd for C46H73BN3OSi2Y: C,
66.57; H, 8.73; N, 4.85. Found: C, 66.77; H, 8.55; N, 5.02.
Reaction of 7 with [PhNMe2H[B(C6F5)4]. C6D5Br (0.6 mL) was added to a mixture of 7
(5.3 mg, 10 μmol) and [PhNMe2H][B(C6F5)4] (8.0 mg, 10 μmol) and the resulting solution
was transferred to an NMR tube equipped with a Teflon (Young) valve. NMR analysis
indicated a clean conversion to the corresponding cationic dibenzyl species, toluene, and free
Chapter 3
52
PhNMe2. 1H NMR (500 MHz, C6D5Br, 40 ˚C) δ: 7.09 (t, 4H, JHH = 7.4 Hz, m-H Ph), 6.92 (d,
4H, JHH = 6.8 Hz, o-H Ph), 6.74 (t, 2H, JHH = 7.4 Hz, p-H Ph), 2.73 (m, 2H, α-H Py), 2.41 (d,
2H, JHH = 13.8 Hz, CCH2), 2.23 (br, 4H, ScCH2), 2.15 (m, 2H, Py α-H), 2.10 (s, 6H, NCH3),
1.83 (d, 2H, JHH = 13.8 Hz, CCH2), 1.82 (m, 2H, NCH2), 1.77, (m, 2H, β-H Py), 1.58 (m, 2H,
Py β-H), 0.36 (s, 3H, CCH3). {1H}13C NMR (125.7 MHz, C6D5Br, 40 ˚C) δ: 148.5 (d, JCF =
240.7 Hz, o-C C6F5), 138.3 (d, JCF = 235.0 Hz, p-C Ph), 136.5 (d, JCF = 242.9 Hz, m-C C6F5),
124.2 (br, ipso-C C6F5), 68.7 (NCH2), 64.7 (br, ScCH2), 60.0 (CCH3), 56.9 (NCH2), 49.5
(NCH3), 47.1 (Py α-C), 24.4 (Py β-C), 12.6 (CCH3). The 13C signals of the benzyl aryl
carbons were obscured by the solvent peaks.
Reaction of 8 with [PhNMe2H[B(C6F5)4]. C6D5Br (0.6 mL) was added to a mixture of 8
(12.5 mg, 20 μmol) and [PhNMe2H][B(C6F5)4] (16.0 mg, 20 μmol) and the resulting solution
was transferred to an NMR tube equipped with a Teflon (Young) valve. NMR analysis
indicated a clean conversion to the corresponding cationic dibenzyl species, toluene, and free
PhNMe2. NMR (500 MHz, C6D5Br, 10 ˚C) δ: 7.03 (t, 4H, JHH = 7.5 Hz, m-H Ph), 6.59 (t, 2H,
JHH = 6.8 Hz, p-H Ph), 6.25 (d, 4H, JHH = 7.2 Hz, o-H Ph), 2.62 (m, 2H, NCH2), 2.29 (d, 2H,
JHH = 14.6 Hz, CCH2), 2.08 (s, 6H, NCH3), 2.03 (m, 2H, Py α–H), 1.95 (m, 2H, NCH2), 1.84
(m, 2H, Py α–H), 1.82 (d, 2H, JHH = 14.6 Hz, CCH2), 1.79 (s, 4H, LaCH2), 1.35 (m, 2H, Py
β–H), 1.22 (m, 2H, Py β–H), 0.30 (s, 3H, CCH3). 13C NMR (125.7 MHz, C6D5Br, 10 ˚C) δ:
148.5 (d, JCF = 240.7 Hz, o-C C6F5), 138.3 (d, JCF = 235.0 Hz, p-C Ph), 136.5 (d, JCF = 242.9
Hz, m-C C6F5), 124.2 (br, ipso-C C6F5), 131.5 (d, JCH = 164.0 Hz, m-C Ph), 121.7 (d, JCH =
163.6 Hz, o-C Ph), 117.6 (d, JCH = 156.9 Hz, p-C Ph), 71.7 (t, JCH = 131.7 Hz, LaCH2), 68.4
(t, JCH = 137.4 Hz, CCH2), 61.0 (s, CCH3), 56.1 (t, JCH = 137.9 Hz, NCH2), 49.2 (q, JCH =
137.4 Hz, NCH3), 45.4 (t, JCH = 139.7 Hz, Py α-C), 25.2 (t, JCH = 132.9 Hz, Py β-C), 12.3 (q,
JCH = 127.2 Hz, CCH3). The 13C signal of the benzyl Cipso was obscured by the solvent peaks.
General procedure for catalytic hydroamination/cyclization of aminoalkenes. Stock
solutions (1.0 mol/L in C6D6) of 2,2-diphenylpent-4-en-1-amine (S1) and
N-methylpent-4-en-1-amine (S2) were prepared. In the glovebox, an NMR tube equipped
with a Teflon (Young) valve was charged with the (pre)catalyst (10 μmol), the activator
[PhNMe2H][B(C6F5)4] (10 μmol, where appropriate), and stock solution of substrate (0.5
mL). The NMR tube was taken out and followed by NMR spectrometry. The products were
identified by 1H NMR and GC-MS in comparison with literature data.
Structure Determinations of Compounds 5-10 and 12. These measurements were
performed according to the procedure described for complex 1 in Chapter 2. Crystallographic
data and details of the data collections and structure refinements are listed in Table 3.7 (for
5-8) and Table 3.8 (for 9, 10, and 12).
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
53
Table 3.7. Crystal Data and Collection Parameters of Complexes 5-8.
compound 5 6 7.THF 8
formula C24H58N3ScSi3 C24H58N3YSi3 C37H54N3OSc C33H46LaN3
Fw 517.96 561.91 601.81 623.65
cryst color, habit colorless, block colorless, block colorless, block yellow, platelet
cryst size (mm) 0.53 0.38 0.24 0.41 0.33 0.22 0.34 0.31 0.15 0.54 0.10 0.03
cryst syst orthorhombic orthorhombic triclinic orthorhombic
space group Pbca Pbca P-1 Pna21
a (Å) 18.668(2) 17.211(1) 9.5975(9) 17.907(3)
b (Å) 17.479(2) 17.984(2) 9.7793(9) 12.848(2)
c (Å) 19.473(2) 20.309(2) 18.7475(18) 12.995(2)
(deg) 100.6527(16)
(deg) 96.5794(17)
(deg) 106.2471(16)
V (Å3) 6354.0(12) 6286.1(10) 1634.2(3) 2989.8(8)
Z 8 8 2 4
calc, g.cm-3 1.083 1.187 1.223 1.386
µ(Mo Kα), cm-1 3.60 19.85 2.58 14.54
F(000), electrons 2288 2432 652 1288
θ range (deg) 2.55, 27.10 2.26, 26.73 2.63, 26.73 2.76, 26.73
Index range (h, k, l) ±23, ±22, ±24 ±21, ±22, ±25 ±12, ±12, ±:23 -21:22, ±16, ±16
Min and max transm 0.8244, 0.9172 0.4831, 0.6461 0.9509, 0.9623 0.4661, 0.9577
no. of reflns collected 50937 49161 12995 22741
no. of reflns collected 6998 6670 6707 6329
no. of reflns with F0 ≥ 4 σ (F0) 5990 5151 4965 4274
wR(F2) 0.0853 0.0688 0.1258 0.1101
R(F) 0.0352 0.0289 0.0471 0.0512
weighting a, b 0.0427, 2.8215 0.0322, 2.1759 0.0772, 0 0.0142, 0
Goof 1.056 1.039 1.042 0.963
params refined 512 512 382 337
min, max resid dens -0.21, 0.42(6) -0.29, 0.45(7) -0.40, -0.44(6) -0.68, 1.59(12)
T (K) 100(1) 100(1) 100(1) 100(1)
Chapter 3
54
Table 3.8. Crystal Data and Collection Parameters of Complexes 9, 10, and 12.
compound 9 10.0.5(toluene) 12.1.5(toluene)
formula C27H56N3ScSi3 C65.5H132N6O2Si6Y2 BC58.5H87OSi2Sc
Fw 551.97 1382.13 960.29
cryst color, habit colorless, block colorless, needle colorless, platelet
cryst size (mm) 0.47 0.21 0.18 0.51 0.13 0.11 0.44 0.23 0.06
cryst syst monoclinic triclinic triclinic
space group P21/c P-1 P-1
a (Å) 19.383(2) 10.653(1) 13.108(4)
b (Å) 9.901(1) 17.454(2) 14.586(4)
c (Å) 17.926(2) 21.730(2) 15.371(4)
(deg) 80.864(2) 78.892(4)
(deg) 94.332(2) 87.771(2) 83.362(4)
(deg) 85.449(2) 81.160(5)
V (Å3) 3430.4(6) 3975.2(7) 2838.3(13)
Z 4 2 2
calc, g.cm-3 1.069 1.155 1.124
µ(Mo Kα), cm-1 3.37 15.84 2.12
F(000), electrons 1208 1490 1042
θ range (deg) 2.58, 28.28 2.39, 26.02 2.62, 25.03
Index range (h, k, l) ±25, -13:23, -23:22 ±13, ±21, -26:25 -15:13, -14:17,
Min and max transm 0.8737, 0.9417 0.6121, 0.8451 0.9010, 0.9874
no. of reflns collected 30312 30900 15891
no. of reflns collected 8460 15266 9452
no. of reflns with F0 ≥ 4 σ (F0) 6672 10248 4167
wR(F2) 0.0952 0.1154 0.2003
R(F) 0.0416 0.0534 0.0794
weighting a, b 0.0415, 1.0064 0.0423, 0 0.0784, 0
Goof 1.042 0.996 0.926
params refined 531 730 615
min, max resid dens -0.25, 0.42(6) -0.54, 0.80(9) -0.68, 0.61(8)
T (K) 100(1) 100(1) 100(1)
Organo Rare Earth Metal Complexes with fac-κ3 Nitrogen-based Neutral Ligand Precursors
55
3.7 References
1. For reviews, see (a) Edelmann, F. T. Comprehensive Organometallic Chemistry III;
Elsevier: Amsterdam, 2007, Vol. 4, p. 1. (b) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.;
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Tazelaar, C. G. J.; Meetsma, A.; Hessen, B. Organometallics 2007, 26, 1014. (d) Howe, R. G.;
Tredget, C. S.; Lawrence, S. C.; Subongkoj, S.; Cowley, A. R.; Mountford, P. Chem. Commun.
2006, 223. (e) Bambirra, S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc.
2004, 126, 9182 (f) Hayes, P. G.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc. 2003, 125, 2132. (g)
Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2003, 42, 5075. (h) Bambirra, S.; van
Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2001, 637.
3. (a) Liu, Y.; Nishuira, M.; Wang, Y.; Hou, Z. J. Am. Chem. Soc. 2006, 128, 5592. (b) Komeyama,
K.; Kawabata, T.; Takehira, K.; Takaki, K. J. Org. Chem. 2005, 70, 7260. (c) Tazelaar, C. G. J.;
Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics 2004, 23,
936. (d) Nishiura, M.; Hou, Z.; Wakatsuki, Y.; Yamaki, T.; Miyamoto, T. J. Am. Chem. Soc.
2003, 125, 1184.
4. (a) Wang, Q.; Xiang, L.; Song, H.; Zi, G. Inorg. Chem. 2008, 47, 4319. (b) Yuen, H. F.; Marks, T.
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V.; Hultzsch, K. C.; Hampel, F. J. Am. Chem. Soc. 2006, 128, 3748. (f) Kim, J. Y.; Livinghouse,
T. Org. Lett. 2005, 7, 4391. (g) Kim, Y. K.; Livinghouse, T.; Horino, Y. J. Am. Chem. Soc. 2003,
125, 9560.(h) Hong, S.; Tian, S.; Metz, M. V.; Marks, T. J. J. Am. Chem. Soc. 2003, 125, 14768.
(i) Li, W.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 1757. (j) Li, W.; Marks, T. J. J. Am. Chem.
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L.; Marks, T. J. Organometallics 1992, 11, 2003. (l) Gagné, M. R.; Marks, T. J. J. Am. Chem.
Soc. 1989, 111, 4108.
5. (a) Kawaoka, A. M.; Douglass, M. R.; Marks, T. J. Organometallics 2003, 22, 4630. (b)
Douglass, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 2001, 123, 10221. (c) Douglass,
M. R.; Marks, T. J. J. Am. Chem. Soc. 2000, 122, 1824.
6. (a) Robert, D.; Trifonov, A. A.; Voth, P.; Okuda, J. J. Organomet. Chem. 2006, 691, 4393. (b)
Horino, Y.; Livinghouse, T. Organometallics 2004, 23, 12. (c) Tardif, O.; Nishiura, M; Hou, Z.
Tetrahedron 2003, 59, 10525. (d) Trifonov. A. A.; Spaniol, T. P.; Okuda, J. Organometallics
2001, 20, 4869. (e) Molander, G. A.; Dowdy, E. D.; Noll, B. C. Organometallics 1997, 17, 3754.
(f) Yu, P. F.; Brard, L.; Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 7157. (g) Molander, G.
A.; Julius, M. J. Org. Chem. 1992, 57, 6347. (h) Sakakura, Y.; Lautenschlager, H. J.; Tanaka, M.
J. J. Chem. Soc., Chem. Commun. 1991, 40.
Chapter 3
56
7. (a) Lukesova, L.; Ward, B. D.; Bellermin-Laponnaz, S.; Wadepohl, H.; Gade, L. H.
Organometallics 2007, 26, 4652. (b) Lukesova, L.; Ward, B. D.; Bellermin-Laponnaz, S.;
Wadepohl, H.; Gade, L. H. Dalton Trans. 2007, 920. (c) Ward, B. D.; Bellemin, L. S.;Gade, L.
H. Angew. Chem., Int. Ed. 2005, 44, 1668. (d) Tredget, C. S.; Lawrence, S. C.; Ward, B. D.;
Howe, R. G.; Cowley, A. R.; Mountford, P. Organometallics 2005, 24, 3136. (e) Lawrence, S. C.;
Ward, B. D.; Dubberley, S. R.; Kozak, C. M.; Mountford, P. Chem. Commun. 2003, 2880. (f)
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Organometallics 2008, 27, 1501. (b) Carver, C. T.; Montreal, M. J.; Diaconescu, P. L.
Organometallics 2008, 27, 363. (c) Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics,
2006, 25, 3454.
9. Bambirra, S.; Tsurugi, H; van Leusen, D.; Hessen, B. Dalton Trans. 2006, 1157.
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11. Bambirra, S.; Meetsma, A.; Hessen, B. Acta Crystallogr., 2006, E62, m314.
12. Shannon, R. D. Acta Crystallogr. Sect. A 1976, 32, 751.
13. (a) Evans, W. J.; Perotti, J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005, 127, 3894. (b) Booij, M.;
Meetsma, A.; Teuben, J. H. Organometallics 1991, 10, 3246.
14. Tsurugi, H.; Matsuo, Y.; Yamagata, T.; Mashima, K. Organometallics, 2004, 23, 2797.
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16. (a) Bambirra, S.; Meetsma, A.; Hessen, B.; Bruins, A. P. Organometallics 2006, 25, 3486. (b)
Bambirra, S.; Boot, S. J.; van. Leusen, D.; Meetsma, A.; Hessen, B. Organometallics 2004, 23,
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Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
57
Chapter 4 Scandium and Yttrium Alkyl Complexes with
fac-κ3 1,4-Diazepan-6-amido Ligands
4.1 Introduction
Organometallic complexes of rare earth metals are an emerging class of catalytically
active species for olefin polymerization and other transformations.1 Although a range of
ancillary ligand types has been used to stabilize these species,2-6 little is known about ligand
effects on catalyst performance and stability. Monoanionic nitrogen-based fac-κ3 ligands
have seen very limited service thus far in organo rare earth metal chemistry.6a,d Deprotonated
diisopropyl-1,4,7-triazacyclononane was reported as monoanionic ligand for both main
group and transition metals,7 but provides very little protection for the N(amide)-M bond.
In chapter 3, we showed that the 1,4,6-trimethyl-1,4-diazepan-6-amine moiety can be
successfully used as a neutral 6-electron donor ancillary ligand framework for neutral and
cationic organo rare earth metal chemistry. It was observed that alkylation of the imino
functionality in the neutral 1,4-diazepan-6-imino ligand L2 can convert it to the monoanionic
1,4-diazepan-6-amido ligand L19. The framework also allows the facile synthesis of
1,4-diazepan-6-amine derivative ligands like HL3 and HL4, that have a secondary amine
group that is readily deprotonated and a substituent on that nitrogen that is easily varied (their
synthesis is described in Chapter 2). In this chapter, we describe the application of these
monoanionic 1,4-diazepan-6-amido ligands (Chart I) to organoscandium and yttrium
chemistry. It is seen that the amide substituent pattern has a great influence on the stability
and catalytic properties of the derived scandium dialkyl complexes. This study also reveals
that there are accessible pathways for ligand decomposition by metalation of the methyl
group on the amido nitrogen in ligand L3 and by ring-opening reactions of the 1,4-diazepane
ring.
Chart I. Ligands Employed in this Chapter.
Chapter 4
58
4.2 Reaction of One Equivalent of Ligand Precursor HL with Metal
Alkyl Precursors
4.2.1 Synthesis and Characterization of Scandium and Yttrium Dialkyl Complexes (L)M(CH2SiMe3)2(THF) (L = L3 and L4; M = Sc and Y)
Reaction of the ligand precursors HL3 and HL4 with the group 3 metal trisalkyls
M(CH2SiMe3)3(THF)2 (M = Sc and Y),8 as shown in Scheme 4.1, afforded dialkyl complexes
(L)M(CH2SiMe3)2(THF) (L = L3, M = Sc, 14; L = L4, M = Sc, 15; L = L4, M = Y, 16) as pale
yellow crystals after crystallization (yield: 14, 78% from toluene/THF; 15, 83% from pentane;
16, 81% from toluene/hexane). No well-defined species were isolated for the reaction of HL3
with Y(CH2SiMe3)3(THF)2. The ambient temperature 1H NMR spectrum of 14 in THF-d8
shows a single resonance for the four methylene protons of the CH2SiMe3 groups (δ -0.85
ppm, 13C δ 30.9 ppm, JCH = 97 Hz), whereas for 15 two doublets are seen (δ -0.32 and -0.51
ppm, JHH = 10.7 Hz, 13C δ 35.2 ppm, JCH = 98 Hz). This suggests that, in THF solvent, the
complex with the least sterically demanding amide substituent more readily inverts the
configuration of the metal center. The YCH2 protons in 16 are diastereotopic: their 1H NMR
resonances are at δ -0.55 and -0.79 ppm with JHH = 11.4 Hz and the corresponding 13C
resonance is found at δ 30.3 ppm with JYC = 37.9 Hz.
Scheme 4.1. Synthesis of Scandium and Yttrium Dialkyl Complexes.
Compounds 14-16 were characterized by single-crystal X-ray diffraction and their
structures are shown in Figure 4.1, with selected bond lengths and bond angles in Table 4.1.
All three compounds contain a monoanionic fac-tridentate ligand in which the nitrogen N(3)
on the 6-position of the 1,4-diazepane moiety is an amide. The THF molecule is located in a
trans position relative to the amide nitrogen. The geometry of the amido nitrogen in 15 and
16 is essentially planar (the sum of angles ΣN(3) is 359.85(10)º and 359.99(16)º for 15 and 16,
respectively), while the geometry in 14 deviates significantly from planarity (the sum of
angles ΣN(3) is 350.7(3)º). One remarkable structural feature of 14 is the large difference of
0.276 Å between the two Sc-N(amine) distances. In fact, the distance Sc-N(2) of 2.710(3) Å
is easily the longest Sc-N(amine) distance reported thus far.9 This extreme elongation seems
to be associated with the trans orientation of one of the alkyl groups relative to this amine:
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
59
N(2)-Sc-C(14) = 172.09(12)º.10 In 15, the larger amide substituent changes the placement of
the alkyl groups to the extent that now the corresponding angle N(1)-Sc-C(21) = 162.43(5)o
is smaller, and the trans Sc-N(1) distance is less elongated. Additionally, the Sc-O distance in
14 is 0.05 Å longer than in 15. The structures of compound 15 and 16 are isomorphous;
comparing the average M-N and M-C distances for Sc and Y analogues indicates that those
for scandium are 0.14-0.15 Å shorter than those for yttrium, corresponding to the difference
in ionic radius between six-coordinated scandium (0.75 Å) and yttrium (0.90 Å).11
Figure 4.1. Molecular Structures of 14 (left), 15 (middle), and 16 (right). Hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Table 4.1. Geometrical Data of Complexes 14, 15, and 16.
14 15 (M = Sc) 16 (M = Y)
Sc-N(1) 2.434(3) M-N(1) 2.5114(13) 2.645(2)
Sc-N(2) 2.710(3) M-N(2) 2.4404(12) 2.572(2)
Sc-N(3) 2.040(3) M-N(3) 2.1100(12) 2.254(2)
Sc-O 2.274(3) M-O 2.3228(11) 2.4299(18)
Sc-C(10) 2.282(4) M-C(17) 2.2612(16) 2.424(2)
Sc-C(14) 2.273(4) M-C(21) 2.2936(14) 2.444(2)
N(1)-Sc-C(10) 145.82(12) N(1)-M-C(21) 162.43(5) 160.70(8)
N(2)-Sc-C(14) 172.09(12) N(2)-M-C(17) 161.66(5) 158.42(8)
N(3)-Sc-O 158.80(13) N(3)-M-O 158.02(4) 152.44(7)
4.2.2 Thermal Stability of the Scandium Dialkyl Compounds
Upon standing in toluene-d8 solution at ambient temperature for about 8 h, complex
14 decomposed cleanly to a single organometallic product with release of 1 equiv of SiMe4 and 1 equiv of THF. This product was obtained in 68% isolated yield by simply
Chapter 4
60
dissolving 14 in toluene at ambient temperature (Scheme 4.2), followed by removal of the volatiles and crystallization from a toluene/pentane mixture. Single-crystal X-ray diffraction (Figure 4.2; the geometrical data are listed in Table 4.2) showed that it can
be formulated as {[CH2(μ-N)-1,4,6-trimethyl-1,4-diazepane]Sc(CH2SiMe3)}2 (17), derived from metalation of the amide methyl substituent.12 The NCH2Sc methylene
proton resonances of 17 are found at δ 2.07 and 1.29 ppm (d, JHH = 7.2 Hz), whereas the methylene proton resonances for the remaining CH2SiMe3 group are found at δ
-0.31 and -0.64 ppm (d, JHH = 11.2 Hz). The NCH2Sc carbon resonance (δ 53.5 ppm, JCH = 130 Hz) is shifted significantly downfield relative to the ScCH2SiMe3 group (δ
19.9 ppm, JCH = 100 Hz).
Scheme 4.2. Thermal Decomposition of the Scandium Dialkyl Complex 14.
Figure 4.2. Molecular structure of 17. Hydrogen atoms are omitted and thermal ellipsoids are drawn at the 50% probability level.
The structural analysis of 17 shows it to be a binuclear complex with the amide nitrogen atoms bridging the two scandium centers. The geometry around each Sc
center is approximately octahedral. The core of the structure is the 4-membered ring Sc(1)-N(6)-Sc(2)-N(3), that is essentially planar (max. deviation from the plane 0.015
Å), annelated with two 3-membered rings (Sc(1)-N(6)-C(22) and Sc(2)-C(9)-N(3)) trans relative to each other. The angles between these two rings and the core plane are
105.44° and 113.60° respectively. For the Sc(1) center, the Sc(1)-C(22) distance in the
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
61
3-membered ring is 0.126(3) Å shorter than the Sc(1)-C(10) distance, while for the
Sc(2) center, the Sc(2)-C(9) bond in the 3-membered ring is 0.124(3) Å longer than the
Sc(2)-C(23) bond. The bond distances Sc-N(bridging amide) in compound 17 are longer than the Sc-N(amide) distances and shorter than the Sc-N(amine) distances in
compound 14.
Table 4.2. Geometrical Data of Complex 17.
Bond Length (Å)
Sc(1)-N(1) 2.5000(19) Sc(2)-N(3) 2.1098(19)
Sc(1)-N(2) 2.3652(19) Sc(2)-N(4) 2.479(2)
Sc(1)-N(3) 2.1943(19) Sc(2)-N(5) 2.4255(17) Sc(1)-N(6) 2.1119(19) Sc(2)-N(6) 2.1908(19)
Sc(1)-C(10) 2.328(3) Sc(2)-C(9) 2.190(3) Sc(1)-C(22) 2.202(3) Sc(2)-C(23) 2.314(3)
Bond Angles (deg) N(1)-Sc(1)-C(22) 155.25(8) N(4)-Sc(2)-C(9) 160.27(8)
N(2)-Sc(1)-N(6) 126.69(7) N(3)-Sc(2)-N(5) 124.74(7) N(3)-Sc-C(10) 147.06(8) N(6)-Sc(2)-C(23) 146.77(8)
N(3)-Sc(1)-N(6) 82.64(7) Sc(1)-N(3)-Sc(2) 96.96(7) Sc(1)-C(10)-Si(1) 125.62(12) Sc(2)-C(23)-Si(2) 120.24(12)
Scheme 4.3. Synthesis of Complex 18.
Although compound 15 also readily loses its coordinated THF molecule (it could be
converted to the THF-free dialkyl compound (L2)Sc(CH2SiMe3)2 (18) by simply pumping a
toluene solution of 15 to dryness, Scheme 4.3), the resulting dialkyl complex 18 is stable at
ambient temperature in toluene solution for at least one day. On a preparative scale, 18 was
obtained as pale yellow powder in 95% yield by reaction of HL4 with Sc(CH2SiMe3)3(THF)2
in toluene, followed by removal of the volatiles. The observations made above show that the
stability of the scandium dialkyl compounds is greatly affected by the nature of the amide
substituent. Different from the scandium dialkyl complexes 14 and 15, the yttrium complex
16 does not lose the coordinated THF molecule and is stable in toluene at room temperature
for at least one day.
Chapter 4
62
4.2.3 Generation of Ionic Scandium Monoalkyl Complexes
The dialkyl compounds 14 and 15 can be converted in THF solvent to the monoalkyl
cations [(L)Sc(CH2SiMe3)(THF)2]+ by reaction with [PhNMe2H][B(C6H5)4] (Scheme 4.4).
The ionic compounds [(L)Sc(CH2SiMe3)(THF)2]+[B(C6H5)4]
- (L = L3, 19; L = L4, 20) were
isolated as analytically pure white microcrystalline powders by layering their THF solutions
with apolar solvents (yield: 19, 82% from n-hexane/THF; 20, 67% from toluene/THF). The 13C NMR resonance of the ScCH2 group in 19 (δ 34.0 ppm) shows a typical downfield shift,
relative to its dialkyl precursor 14 (δ 30.9 ppm), associated with conversion to a cationic
species.3b,f The compounds contain two THF molecules per Sc center, as seen by elemental
analysis. Their room temperature 1H NMR spectra show broad resonances, indicating
fluxionality. Cooling THF-d8 solutions of compound 19 or 20 to -50 °C slows down this
dynamic process, revealing an asymmetric structure consistent with a cis-configuration of the
two strongest σ–donors in the complex (alkyl and amide).
Scheme 4.4. Synthesis of Ionic Scandium Monoalkyl Complexes 19 and 20.
Scheme 4.5. Reaction of 17 with Ethylene – Synthesis of 21.
4.2.4 Reactivity of Scandium Alkyl Complexes towards Ethylene
When a toluene solution of the dinuclear complex 17 was exposed to 1 bar of ethylene, one
molecule of ethylene per scandium was selectively inserted into the Sc-CH2N bond to give
the complex {[CH2CH2CH2(μ-N)-1,4,6-trimethyl-1,4-diazepine]Sc(CH2SiMe3)}2 (21,
Scheme 4.5) within 3 h at room temperature. This indicates that the Sc-C bond in the Sc-C-N
3-membered ring is more reactive than the Sc-CH2SiMe3 bond. Complex 21 was isolated as
colorless crystalline material in a yield of 71% by recrystallization from a toluene/pentane
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
63
solution. The identity of complex 21 was confirmed by a combination of 1D and 2D (COSY
and HSQC) NMR techniques and single-crystal X-ray diffraction (Figure 4.3; the
geometrical date are compiled in Table 4.3). The Sc- and N-methylene protons of the
ScCH2CH2CH2N moiety are diastereotopic and their 1H resonances are found at δ 0.93 and
0.76 ppm and δ 3.53 and 1.70 ppm (JHH is not resolved due to overlap), respectively. The
corresponding 13C NMR resonances are at δ 47.9 and 56.0 ppm, respectively. For the
remaining trimethylsilylmethyl group, the methylene 1H and 13C NMR resonances are found
at δ -0.42 and 0.69 ppm and δ 32.1 ppm.
The structural analysis of compound 21 shows it to be a binuclear complex with amide
nitrogen bridging the two scandium centers and the geometry around each scandium center is
approximately octahedral. The core of the structure is the 4-membered ring
Sc(1)-N(6)-Sc(2)-N(3), which is similar with compound 17, but it is more twisted with a max.
deviation from the least-squares plane of 0.14 Å. The two five-membered rings
(Sc(1)-N(6)-C(24)-C(25)-C(26) and Sc(2)-N(3)-C(9)-C(10)-C(11)) are annelated with the
4-membered core. Interestingly, the remaining two alkyl groups now have a cis arrangement
relative to the core plane (in contrast to the trans arrangement in 17). The Sc-N bond lengths
to the bridging nitrogen atom in complex 21 are on average longer than in compound 17.
Figure 4.3. Molecular structure of 21. Hydrogen atoms are omitted and thermal ellipsoids are drawn at the 50% probability level.
Catalytic ethylene polymerization experiments in toluene solvent using the THF
complexes 14 or 15 in conjunction with [PhNMe2H][B(C6F5)4] activator did not show any
activity. In contrast, the combination of the THF-free dialkyl compound 18 with
[PhNMe2H][B(C6F5)4] afforded an active, single-site ethylene polymerization catalyst, with
a productivity of 584 kg(PE)(molSc)-1h-1bar-1 (toluene solvent, 5 bar, 50 °C, 10 min run time),
producing PE with Mw = 1.2 × 106, Mw/Mn = 1.9. Thus it appears that even a single THF
molecule can shut down the catalytic activity, suggesting that the actual active species is a
THF-free (6-amido-1,4,6-trimethyl-1,4-diazepane)Sc(alkyl) cation.
Chapter 4
64
Table 4.3. Geometrical Data of Complex 21.
Bond Length (Å)
Sc(1)-N(1) 2.5000(19) Sc(2)-N(3) 2.1098(19)
Sc(1)-N(2) 2.3652(19) Sc(2)-N(4) 2.479(2)
Sc(1)-N(3) 2.1943(19) Sc(2)-N(5) 2.4255(17) Sc(1)-N(6) 2.1119(19) Sc(2)-N(6) 2.1908(19)
Sc(1)-C(10) 2.328(3) Sc(2)-C(9) 2.190(3) Sc(1)-C(22) 2.202(3) Sc(2)-C(23) 2.314(3)
Bond Angles (deg) N(1)-Sc(1)-C(22) 155.25(8) N(4)-Sc(2)-C(9) 160.27(8)
N(2)-Sc(1)-N(6) 126.69(7) N(3)-Sc(2)-N(5) 124.74(7) N(3)-Sc-C(10) 147.06(8) N(6)-Sc(2)-C(23) 146.77(8)
N(3)-Sc(1)-N(6) 82.64(7) Sc(1)-N(3)-Sc(2) 96.96(7) Sc(1)-C(10)-Si(1) 125.62(12) Sc(2)-C(23)-Si(2) 120.24(12)
4.3 Reaction of Two Equivalent of Ligand Precursor HL with Metal
Alkyl Precursors
4.3.1 Ring Opening of 1,4-diazepane Ligand by Yttrium Alkyl Complexes
The rare earth metal tribenzyl complexes M(CH2Ph)3(THF)3 have recently emerged as
convenient organometallic starting materials,13 and the possibility of multihapto bonding of
the benzyl group to the metal center can impart additional stability to organo rare earth
metal complexes with low coordination number.14 Reaction of Y(CH2Ph)3(THF)3 with 1
equiv of HL4 was first carried out on an NMR tube scale in C6D6 and the NMR spectra
indicated the formation of (L4)Y(CH2Ph)2(THF). The 1H NMR resonance of YCH2 is found
at δ 2.07 ppm and the corresponding 13C resonance is at δ 53.5 ppm with JYC = 30.8 Hz.
Nevertheless, attempts to isolate this yttrium dibenzyl complex resulted in a sticky material
that could not be redissolved in C6D6. 1H NMR spectroscopy of this material in THF-d8
indicated the formation of a complicated mixture of ill-defined species. Apparently
(L4)Y(CH2Ph)2(THF) is less stable than its trimethylsilylmethyl congener 16. This might be
due to the lower degree of steric shielding that the benzyl group provides relative to the
trimethylsilylmethyl group.
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
65
Scheme 4.6. Ring-opening Reaction of L4 -- Synthesis of 22.
To see whether (L4)Y-benzyl species might be stabilized by binding a second ligand L4,
(L4)Y(CH2Ph)2(THF) (generated in-situ in C6D6 as described above) was reacted with an
additional equiv of HL4. This afforded a single organometallic species with concomitant
release of 2 equiv of toluene. A single-crystal X-ray diffraction study on the isolated
material (Figure 4.4, the geometrical data are listed in Table 4.4) showed that it can be
formulated as (L4)Y{PhMe2SiNC(Me)(CH2NMe)[CH2N(Me)CH=CH2]} (22 in Scheme
4.6). On a preparative scale, complex 22 was obtained as a colorless crystalline solid
(isolated yield: 74%) by reaction of Y(CH2Ph)3(THF)3 with 2 equiv of HL4 in toluene at
room temperature, followed by removal of all the volatiles and recrystallization from a
toluene/n-hexane solution.
Figure 4.4. Molecular structure of 22. Hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
The structure of 22 reveals a complex with a 6-coordinated yttrium center in an
approximately octahedral geometry, containing a monoanionic fac-tridentate 1,4-diazepane
ligand L4 and a new dianionic tridentate ligand, which is formed by an 1,4-diazepane
ring-opening reaction of ligand L4. The ethylene unit of the 1,3-diazepane ring in ligand L4
has been converted to a vinyl group with a C(17)-C(18) bond distance of 1.326(5) Å. The
metal center displays two short yttrium-N(amido) bonds (Y-N(5) = 2.264(3) Å, Y-N(6) =
2.194(3) Å) and a longer yttrium-N(amino) bond (Y-N(4) = 2.709(2) Å) with the new
tridentate ligand, consistent with diamido-amino ligand character.
Chapter 4
66
Table 4.4. Geometrical Data of Complex 22.
Bond Length (Å)
Y-N(1) 2.5000(19) Y-N(4) 2.1098(19)
Y-N(2) 2.3652(19) Y-N(5) 2.479(2)
Y-N(3) 2.1943(19) Y-N(6) 2.4255(17) C(5)-C(6) 2.1119(19) C(17)-C(18) 2.1908(19)
Bond Angles (deg) N(1)-Y-N(4) 164.89(9) N(2)-Y-N(5) 170.40(8)
N(3)-Y-N(6) 157.9(1)
The solution NMR spectra of 22 in C6D6 are consistent with the structure as determined by
X-ray diffraction. The 1H NMR spectrum indicates a fully asymmetrical structure, as seen e.g.
by four resonances for the SiMe-groups (δ 0.89, 0.79, 0.78, 0.73 ppm). Four N-Me
resonances are found, with that of the MeN(amido) group (δ 3.21 ppm) downfield shifted
relative to the MeN(amino) resonances (δ 2.31, 2.34, and 2.11 ppm). The vinyl group in 22
exhibits 1H NMR resonances at δ 6.39 ppm (dd, JHH = 8.6 Hz and 15.8 Hz, CH=CH2) and at δ
3.95 and 3.86 ppm (d, JHH = 8.6 Hz and 15.8 Hz, respectively, CH=CH2), with the
corresponding 13C NMR resonances at δ 150.9 ppm (d, JCH = 170.1 Hz) and δ 91.4 ppm (t,
JCH = 161.1 Hz).
Scheme 4.7. Proposed Pathway of Ring-opening of Ligand L4.
All attempts to observe well-defined intermediates in the formation of 22 by in-situ NMR
spectrometry were unsuccessful. A proposal for the ring-oprning of ligand L4 to give 22 is
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
67
shown in Scheme 4.7. (L4)Y(CH2Ph)2(THF) reacts with ligand HL4 to give the
bis(ligand)-Y-monobenzyl complex (A) (in this intermediate, one of the ligands might be
bonded to the metal through two of the three nitrogen atoms, see the structure of 24 described
below). Intramolecular metalation of the ethylene unit in L4 gives the intermediate B with a
Y-N-C-C metallocycle unit. Subsequent β-nitrogen elimination in this metallocycle then
generates an Y-N(amido) bond and a vinylamine. Cyclometalation followed by β-nitrogen
elimination was earlier seen to be involved in the thermal decomposition of cationic organo
rare earth metal complexes supported by isopropyl-substituted triazacyclononane-amido
ligands.15
In contrast to the reactivity of the (L4)-Y-dibenzyl system described above, reaction of the
yttrium dialkyl complex 16 with HL4 does not take place, even at 50 ºC. This might be due to
the greater steric demand of the trimethylsilylmethyl groups. In line with this, reaction of 16
with the smaller HL3 in C6D6 does go to completion at 50 ºC. It generates selectively a single
Y-complex, accompanied by the release of 2 equiv of TMS and 1 equiv of free THF. The
same Y-species is formed in the reaction of in-situ generated (L4)Y(CH2Ph)2(THF) with HL3.
The resulting Y-species was characterized by single-crystal X-ray diffraction (Figure 4.5, the
geometrical data are compiled in Table 4.5) and can be formulated as
(L4)Y[CH2=CHN(Me)C(Me)(CH2NMe)2] (23, Scheme 4.8). Complex 23 was obtained on a
preparative scale as a colorless crystalline solid (isolated yield: 78%) by reaction of 16 with
HL3 in toluene at 50 ºC. Complex 23 contains two ligands; ligand L4, coordinated to yttrium
in the same way as in complex 16, and a new diamido-amino tridentate ligand derived from
ligand L3 by ring-opening followed by a shift of the resulting vinyl group to what was the
exocyclic nitrogen atom in L3.
Scheme 4.8. Reaction of 16 with Ligand Precursor HL3.
The solution NMR spectra of 23 in C6D6 are consistent with the structure as determined by
X-ray diffraction. The 1H NMR spectrum shows a fully asymmetric structure; for example,
five N-Me resonances are found, with those at δ 3.26 and 3.24 ppm assigned to Me-N(amido)
and those at δ 2.26, 2.19, and 2.11 ppm assigned to Me-N(amino). The vinyl group in 23
exhibits 1H NMR resonances at δ 6.52 ppm (dd, JHH = 9.0 Hz and 15.6 Hz, CH=CH2) and at
δ 4.14 and 4.05 ppm (d, JHH = 9.0 Hz and 15.6 Hz, respectively, CH=CH2), with the
corresponding 13C resonances at δ 144.5 ppm (d, JCH = 175.0 Hz) and δ 93.7 ppm (t, JCH =
Chapter 4
68
157.5 Hz). Although NMR studies on 23 indicate an asymmetric structure in solution, only a
single resonance (δ 0.76 ppm for 1H and 1.83 ppm for 13C) was observed for the two methyl
groups on silicon, which might be due to accidental degeneracy.
Figure 4.5. Molecular structure of 23. All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 30% probability level.
Table 4.5. Geometrical Data of Complex 23.
Bond Length (Å)
Y-N(1) 2.194(6) Y-N(4) 2.585(7)
Y-N(2) 2.203(5) Y-N(5) 2.588(7) Y-N(3) 2.668(3) Y-N(6) 2.262(5)
C(8)-C(9) 2.203(18) C(11)-C(12) 2.424(19) Bond Angles (deg)
N(1)-Y-N(5) 152.2(2) N(2)-Y-N(4) 164.0(2) N(3)-Y-N(6) 169.90(17)
A possible pathway of the formation of 23 is depicted in Scheme 4.9. After initial reaction
of 16 with HL3, ring-opening of ligand L3 (following the pathway described for the
formation of 22 in Scheme 4.7) generates the intermediate C. This intermediate can then
rearrange to give 23 via 1,4-vinyl shift. This 1,4-vinyl shift may take place via a two-step
process; the first step is the formation of D by intramolecular insertion of the vinyl group in C
into one of the Y-N(amido) bonds, a step well-documented in intramolecular
hydroamination/cyclization reactions catalyzed by rare earth metal complexes.16 The second
step is β-nitrogen elimination in the Y-C-C-N metallacycle unit of D to give the final product
23. The proposed intermediates C and D could not be observed, suggesting that the initial
ring-opening reaction of L3 is the rate-limiting step in the process.
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
69
Scheme 4.9. Proposed Pathway for the Formation of 23.
Scheme 4.10. Synthesis of Bis(Ligand)-Y-Monoalkyl Complex 24.
4.3.2 Synthesis of a Bis(ligand) Supported Yttrium Monoalkyl Compound.
Although bis(ligand)-Y-monoalkyl species are proposed as initially formed intermediates
in the ring-opening processes described above, we could not unequivocally observe or isolate
them. Nevertheless, in one case were we able to isolate such a species, when a combination of
ligand L3 and L19 was used together with trimethylsilylmethyl as the Y-alkyl group. Reaction
of (L19)Y(CH2SiMe3)2(THF) (10, described in Chapter 3) with 1 equiv of HL3 afforded the
yttrium monoalkyl compound (L3)(L19)YCH2SiMe3 (24) as a colorless solid in 82% isolated
yield after crystallization from a toluene/pentane mixture (Scheme 4.10). The ambient
temperature 1H NMR spectra in C6D6 show broad resonances, indicating fluxionality.
Chapter 4
70
Cooling a toluene-d8 solution of complex 24 to -30 ˚C slows down this dynamic process,
revealing a fully asymmetric structure as seen from the four separate resonances (δ 2.30, 2.20,
2.05, and 2.04 ppm) for the methyl groups on amino-nitrogen atoms. The YCH2 resonances
are diasterotopic and found at δ -0.04 and -1.06 ppm (JHH = 10.3 Hz, JYH not resolved), and
the corresponding 13C NMR resonance is found at δ 22.5 ppm with JYC = 40.7 Hz.
Figure 4.6. Molecular structure of 24. Hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
The structure of 24 was determined by single-crystal X-ray diffraction and is shown in
Figure 4.6 (the geometrical data are listed in Table 4.6). The yttrium-center is 6-coordinate in
an approximately octahedral geometry. The ligand L19 is facially bound to yttrium via three
nitrogen atoms: a short bond to N(amido) (Y-N(1) = 2.228(4) Å) and two Y-N(amino) bonds
of unequal length (Y-N(2) = 2.589(5), Y-N(3) = 2.821(4) Å). The ligand L3 is bound to
yttrium via only two nitrogen atoms; Y-N(amido) (Y-N(6) = 2.227(5) Å) and Y-N(amino)
(Y-N(4) = 2.600(6) Å); the second amine group of this ligand is not coordinated.
Table 6. Geometrical Data of Complex 24.
Bond Length (Å)
Y-N(1) 2.228(4) Y-N(4) 2.600(6) Y-N(2) 2.589(5) Y-N(6) 2.227(5)
Y-N(3) 2.821(4) Y-C(18) 2.473(6) Bond Angles (deg)
N(1)-Y-N(4) 163.99(17) N(2)-Y-N(6) 146.91(16) N(3)-Y-C(18) 153.00(17) Y-C(18)-Si(1) 138.6(3)
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
71
Scheme 4.11. Thermolysis of Complex 24.
To see whether bis(ligand)-Y-monoalkyl compounds are intermediates involved in the
ring-opening processes described above, the thermolysis of yttrium monoalkyl complex 24
was studied on an NMR-tube scale (Scheme 4.11). Upon standing in C6D6 solution at 80 C
for about 6 h, complex 24 fully decomposed and two organometallic species bearing vinyl
groups were observed by NMR spectrometry. The 1H resonances of the vinyl groups in these
two species show similarity to those of the vinyl group in 23; One set of 1H resonances for
vinyl group are present at δ 6.55 ppm (dd, JHH = 9.0 Hz and JHH = 15.7 Hz, CH=CH2) and δ
4.17 and 4.08 ppm (d, JHH = 9.0 Hz and JHH = 15.7 Hz, respectively, CH=CH2) and the other
set at δ 6.55 ppm (dd, JHH = 9.0 Hz and JHH = 15.7 Hz, CH=CH2) and δ 4.15 and 4.06 ppm (d,
JHH = 9.0 Hz and JHH = 15.7 Hz, respectively, CH=CH2). To find out which azepane ligand
decomposes during the thermolysis, the mixture was quenched with D2O and analyzed by
GC-MS. Only DL19 (not DL3) was detected by GC-MS analysis, indicating that it is L3 that
decomposes selectively. Vinylamine Me(CH2=CH)NC(Me)(CH2NMeD)2 was not observed,
which might be due to its instability once uncoordinated to yttrium. Because ligand L19 is
asymmetric, two diastereomers (with molar ratio of 53/47) are observed for thermolysis of 24
(Scheme 4.11).
Scheme 4.12. Ring-opening of Ligand L3.
4.3.3 Ring Opening of Ligand L3 by Organo Scandium Complexes
As described above, the scandium dialkyl complex (L3)Sc(CH2SiMe3)2(THF) 14
decomposes via metalation of the methyl group on the amido-N in ligand L3 in the absence of
a coordinating solvent like THF. To see whether (L3)Sc-alkyl species might be stabilized by
Chapter 4
72
binding a second L3, the reaction of 14 with additional equiv of ligand HL3 was performed.
This afforded a single organometallic species with the concomitant release of 2 equiv of TMS
and 1 equiv of free THF. A single-crystal X-ray diffraction study on the isolated product
(Figure 4.7, the geometrical data are listed in Table 4.7) indicated that it can be formulated as
(L3)Sc[(CH2=CH)(CH3)NC(CH3)(CH2NCH3)2] (25, Scheme 4.12). The same Sc-species is
formed in the reaction of 17 (generated in situ by decomposition of 14 in C6D6, Scheme 4.2)
with 2 equiv of HL3. On a preparative scale, complex 25 was obtained as a colorless
crystalline solid (isolated yield: 72%) by reaction of Sc(CH2SiMe3)3(THF)2 with 2 equiv of
HL3 at room temperature, followed by removal of all the volatiles and recrystallization from
a toluene/hexane mixture. The vinyl group in 25 exhibits 1H NMR resonances at δ 6.45 ppm
(dd, JHH = 8.9 Hz and JHH= 15.9 Hz, CH=CH2) and δ 4.17 and 4.09 ppm (JHH = 8.9 Hz and
15.9 Hz, respectively, CH=CH2), with the corresponding 13C resonances at δ 144.9 ppm (d,
JCH = 170 Hz) and δ 94.1 ppm (t, JCH = 157 Hz). Complex 25 is formed via ring-opening of
ligand L3 followed by 1,4-vinyl shift, as proposed for the formation of compound 23
(Scheme 4.9).
Figure 4.7. Molecular structure of 25. All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Table 4.7. Geometrical Data of Complex 25.
Bond Length (Å)
Sc-N(1) 2.4892(17) Sc-N(4) 2.0661(17)
Sc-N(2) 2.4617(17) Sc-N(5) 2.0600(17) Sc-N(3) 2.0753(17) Sc-N(6) 2.5438(17)
C(2)-C(3) 1.519(3) C(17A)-C(18A) 1.321(10) Bond Angles (deg)
N(1)-Y-N(5) 163.08(6) N(2)-Y-N(4) 158.64(6) N(3)-Y-N(6) 171.91(6)
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
73
4.4 Concluding Remarks
We have shown that the monoanionic 1,4-diazepan-6-amido ligands L3 and L4 are
suitable to support the scandium dialkyl complexes (L)Sc(CH2SiMe3)2(THF) and the substituent on the amido nitrogen has a significant influence both on their thermal
stability and catalytic properties. These two scandium dialkyl THF adducts readily lose
the coordinated THF molecule; ligand L4 with the PhMe2Si-group on the amido
nitrogen gives a stable THF-free dialkyl complex, whereas (L3)Sc(CH2SiMe3)2(THF) forms a binuclear dialkyl complex via the metalation of the methyl group on the amido
nitrogen of L3 by the Sc-alkyl bond. For catalytic studies, only the THF-free dialkyl complex with L4, upon activation with [PhNMe2H][B(C6F5)4], is active for ethylene polymerization.
We extended the application of ligand L4 to organoyttrium chemistry with two different organoyttrium precursors, Y(CH2SiMe3)3(THF)2 and Y(CH2Ph)3(THF)3, and only use of the former precursor led to the isolation of the thermally stable yttrium
dialkyl complex. Attempts to stabilize the yttrium benzyl species by using two ligands resulted in another route for ligand decomposition by ring-opening reaction of the
1,4-diazepane ring: intramolecular metalation of the ethylene unit in the 1,4-diazepane ring by the Y-benzyl bond in the initially formed bis(ligand) yttrium benzyl species and
subsequent β-nitrogen elimination transforms the monoanionic 1,4-diazepan-6-amido ligands to dianionic acyclic diamido-amino ligands. Additionally, 1,4-vinyl group shift
has been observed for the ring-opening processes of ligand L3. The isolation and thermolysis of yttrium monoalkyl complex (L3)(L19)YCH2SiMe3 confirms the initially formed bis(ligand)-Y intermediate species proposed in the ring-opening processes. Such ligand decomposition was also observed for scandium organometallics when
attempts to prepare bis(ligand)Sc-alkyl complexes.
4.5 Experimental Section
General Remarks. See the corresponding part in Chapter 2. M(CH2SiMe3)3(THF)2 (M =
Sc and Y) 8 and Y(CH2Ph)3(THF)313 were prepared according to published procedures.
Synthesis of (L3)Sc(CH2SiMe3)2(THF) (14). To a solution of Sc(CH2SiMe3)3(THF)2 (626
mg, 1.39 mmol) in THF (20 mL), was added dropwise a solution of HL3 (238 mg, 1.39 mmol)
in THF (20 mL) while stirring. The mixture was stirred at room temperature for 30 min and
then was concentrated to 1 ml under reduced pressure. On top of the resulting yellow solution,
pentane (5 mL) was carefully layered. Upon cooling to -30 °C, crystalline material was
formed, including crystals suitable for X-ray diffraction. The mother liquor was decanted and
the solid was dried under reduced pressure, yielding the title compound (497 mg, 1.08 mmol,
78%) as a pale yellow solid. 1H NMR (400MHz, THF-d8): δ 3.61 (m, 4H, α-H THF), 3.22 (m,
2H, NCH2), 2.86 (s, 3H, CNCH3), 2.85 (d, 2H, JHH = 12.3 Hz, CCH2), 2.50 (m, 2H, NCH2),
Chapter 4
74
2.46 (s, 6H, NCH3), 2.44 (d, 2H, JHH = 12.3 Hz, CCH2), 1.77 (m, 4H, β-H THF), 0.76 (s, 3H,
CCH3), -0.06 (s, 18H, Si(CH3)3), -0.85 (s, 4H, ScCH2). 13C NMR (100.5MHz, THF-d8): δ
77.9 (t, JCH = 134.0 Hz, CCH2), 69.4 (t, JCH = 140.4 Hz, α-C THF), 60.3 (t, JCH = 136.7 Hz,
NCH2), 59.2 (s, CCH3), 51.9 (q, JCH = 135.2 Hz, NCH3), 37.1 (q, JCH = 127.6 Hz, CNCH3),
30.9 (t, JCH = 96.9 Hz, ScCH2), 27.5 (t, JCH = 132.7 Hz, β-C THF), 21.1 (t, JCH = 125.0 Hz,
CCH3), 5.8(q, JCH = 115.5 Hz, Si(CH3)3). Anal. Calcd for C21H50N3OScSi2: C, 54.62; H,
10.91; N, 9.10. Found: C, 54.15; H, 10.84; N, 9.41.
Synthesis of (L4)Sc(CH2SiMe3)2(THF) (15). To a solution of Sc(CH2SiMe3)3(THF)2 (416
mg, 0.92 mmol) in pentane (30 mL), was added dropwise a solution of HL4 (269 mg, 0.92
mmol) in pentane (10 mL) while stirring. The mixture was stirred at room temperature for 30
min and then the mixture was concentrated to 5 mL under reduced pressure. Upon cooling to
-30 °C, crystalline material had formed, including crystals suitable for X-ray diffraction. The
mother liquor was decanted and the solid was dried under reduced pressure yielding the title
compound (445 mg, 0.76 mmol, 83%) as an off-white solid. 1H NMR (400MHz, THF-d8): δ
7.65 (d, 2H, JHH = 6.69 Hz, o-H Ph), 7.19 (t, 2H, JHH = 6.90 Hz, m-H Ph), 7.15 (t, 1H, JHH =
7.44 Hz, p-H Ph), 3.61 (m, 4H, α-H THF), 3.25 (m, 2H, NCH2), 2.81 (d, 2H, JHH = 12.0 Hz,
CCH2), 2.56 (s, 6H, NCH3), 2.49 (m, 2H, NCH2), 2.43 (d, 2H, JHH = 12.0 Hz, CCH2), 1.77 (m,
4H, β-H THF), 0.76 (s, 3H, CCH3), 0.46 (s, 6H, Si(CH3)2), -0.03 (s, 18H, Si(CH3)3), -0.32 (d,
JHH = 10.7 Hz, 2H, ScCH2), -0.51 (d, JHH = 10.7 Hz, 2H, ScCH2). 13C NMR (100.5MHz,
THF-d8): δ 151.1 (s, ipso-C Ph), 135.5 (d, JCH = 155.5 Hz, o-C Ph), 129.1 (d, JCH = 156.6 Hz,
m-H Ph), 129.0 (d, JCH = 157.9 Hz, p-C Ph), 82.4 (t, JCH = 134.1 Hz, CCH2), 69.3 (α-C THF,
JCH unresolved due to overlap with THF-d8), 60.5 (t, JCH = 140.7 Hz, NCH2), 58.1 (s, CCH3),
52.9 (q, JCH = 136.0 Hz, NCH3), 35.2 (t, JCH = 98.1 Hz, ScCH2), 27.6 (β-C THF, JCH
unresolved due to overlap with THF-d8), 26.6 (q, JCH = 124.8 Hz, CCH3), 6.3 (q, JCH = 117.1
Hz, Si(CH3)3), 6.0 (q, JCH = 116.4 Hz, Si(CH3)2). Anal. Calcd for C28H58N3OScSi3: C, 57.78;
H, 10.04; N, 7.22. Found: C, 58.30; H, 10.18; N, 7.15.
Synthesis of (L4)Y(CH2Me3)2(THF) (16). To a solution of Y(CH2SiMe3)3(THF)2 (617.4
mg, 1.25 mmol) in toluene (20 mL), was added a solution of ligand precursor HL4 (363.8 mg,
1.25 mmol) in toluene (2 mL) while stirring and the resulting solution was stirred for another
10 min at room temperature. All the volatiles were removed under reduced pressure and then
the residue was dissolved in toluene (2 mL). Hexane was added until precipitate formed.
Upon cooling to -30 ˚C, crystalline material formed, including crystals suitable for
single-crystal X-ray diffraction. The mother liquor was decanted and the solid was dried
under reduced pressure, yielding the title compound (631.7 mg, 1.01 mmol, 81%) as a
colorless solid. 1H NMR (500 MHz, C6D6): δ 7.93 (d, 2H, JHH = 6.2 Hz, o-H Ph), 7.35 (t, 2H,
JHH = 7.1 Hz, m-H Ph), 7.23 (t, 1H, JHH = 7.1 Hz, p-H Ph), 3.73 (m, 4H, α-H THF), 2.55 (d,
2H, JHH = 11.5 Hz, CCH2), 2.53 (m, 2H, NCH2), 2.17 (s, 6H, NCH3), 1.85 (d, 2H, JHH = 11.5
Hz, CCH2), 1.67 (m, 2H, NCH2), 1.34 (m, 4H, β-H THF), 0.79 (s, 3H, CCH3), 0.73 (s, 6H,
Si(CH3)2), 0.44 (s, 9H, Si(CH3)3), -0.55 (b, 2H, YCH2, JYH not resolved), -0.73 (b, 2H, YCH2,
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
75
JYH not resolved). 13C NMR (125.7 MHz, C6D6): δ 148.3 (s, ipso-C Ph), 134.0 (d, JCH = 156.0
Hz, o-C Ph), 128.3 (d, JCH = 156.0 Hz, p-C Ph), 127.9 (d, JCH = 155.0 Hz, m-C Ph), 80.3 (t,
JCH = 136.4 Hz, CCH2), 70.6 (t, JCH = 146.9 Hz, α-C THF), 58.0 (t, JCH = 134.7 Hz, NCH2),
56.2 (s, CCH3), 50.5 (q, JCH = 136.8 Hz, NCH3), 30.3 (dt, JCH = 97.7 Hz, JYC = 37.9 Hz,
YCH2), 25.7 (q, JCH = 125.4 Hz, CCH3), 25.0 (t, JCH = 134.1 Hz, β-C THF), 5.2 (q, JCH =
116.9 Hz, Si(CH3)3), 4.0 (q, JCH = 117.0 Hz, Si(CH3)2). Anal. Calcd for C28H53N3OSi3Y: C,
53.73, H, 9.34, N, 6.71; Found: C, 53.58, H, 9.42, N, 6.53.
Synthesis of {[CH2(μ-N)-1,4,6-trimethyl-1,4-diazepine]Sc(CH2SiMe3)}2 (17). The
dialkyl compound 14 (270 mg, 585 μmol) was dissolved in toluene (20 mL) at room
temperature and the resulting solution was stirred for 10 min. All the volatiles were removed
under reduced pressure and the residue was dissolved in toluene (1 mL) and pentane was
added until precipitate began to form. Upon cooling to -30 °C, crystalline material formed,
including crystals suitable for X-ray diffraction. The mother liquor was decanted and the
solid was dried under reduced pressure, yielding the title compound (241 mg, 400 μmol, 68%)
as a pale yellow solid. The assignment of NMR resonances was aided by COSY and HSQC
experiments. 1H NMR (500MHz, C6D6): δ 3.13 (d, 2H, JHH = 12.2 Hz, CCHH), 3.05 (m, 2H,
NCH2), 2.89 (d, 2H, JHH = 12.9 Hz, CCHH), 2.53 (s, 6H, NCH3), 2.51 (m, 2H, NCH2), 2.36 (s,
6H, NCH3), 2.07 (d, 2H, JHH = 7.2 Hz, ScCHHN), 1.97 (d, 2H, JHH = 12.2 Hz, CCHH), 1.89
(m, 2H, NCH2), 1.84 (d, 2H, JHH = 12.9 Hz, CCHH), 1.65 (m, 2H, NCH2), 1.29 (d, 2H, JHH =
7.2 Hz, ScCHHN), 0.99 (s, 6H, CCH3), 0.40 (s, 18H, Si(CH3)3), -0.31 (d, 2H, JHH = 11.2 Hz,
ScCHH), -0.64 (d, 2H, JHH = 11.2 Hz, ScCHH). 13C NMR (125.7MHz, C6D6): δ 77.8 (t, JCH =
135.9 Hz, CCH2), 68.2 (t, JCH = 134.2 Hz, CCH2), 60.1 (s, CCH3), 58.8 (t, JCH = 135.6 Hz,
NCH2), 55.6 (t, JCH = 135.6 Hz, NCH2), 53.5 (t, JCH = 129.8 Hz, NCH2Sc), 52.4 (q, JCH =
135.6 Hz, NCH3), 49.1 (q, JCH = 135.6 Hz, NCH3), 19.9 (q, JCH = 125.7 Hz, CCH3), 19.9 (t,
JCH = 100.4 Hz, ScCH2), 5.3 (q, JCH = 115.7 Hz, Si(CH3)3). Anal. Calcd for C26H60N6Sc2Si2:
C, 51.80; N, 13.94; H, 10.03. Found: C, 51.52; N, 13.93; H, 10.03.
Synthesis of (L4)Sc(CH2SiMe3)2 (18). Scandium dialkyl compound 15 (232 mg, 0.40
mmol) was dissolved in toluene (5 mL) and the resulting solution was evaporated to dryness
yielding the title compound (194 mg, 0.38 mmol, 95%) as an off-white solid. 1H NMR (300
MHz, C6D6): δ 7.81 (d, 2H, JHH = 8.06 Hz, o-H Ph), 7.31 (t, 2H, JHH = 7.28 Hz, m-H Ph), 7.21
(t, 1H, JHH = 7.42 Hz, p-H Ph), 2.41 (m, 2H, NCH2), 2.28 (d, JHH = 12.0 Hz, CCH2), 2.11 (s,
6H, N(CH3)2), 1.65 (d, JHH = 12.0 Hz, CCH2), 1.56 (m, 2H, NCH2), 0.76 (s, 6H, Si(CH3)2),
0.59 (s, 3H, CCH3), 0.41 (s, 18H, Si(CH3)3), -0.03 (s, 4H, ScCH2). 13C NMR (75.4 MHz,
C6D6): δ 145.4 (s, ipso-C Ph), 134.1 (d, JCH = 155.2 Hz, o-C Ph), 128.5 (d, JCH = 157.1 Hz,
m-C Ph), 127.9 (d, JCH = 157.1 Hz, m-C Ph), 76.6 (t, JCH = 138.5 Hz, CCH2), 56.9 (t, JCH =
135.5 Hz, NCH2), 54.3 (s, CCH3), 51.3 (q, JCH = 137.5 Hz, NCH3), 35.2 (t, JCH = 100.7 Hz,
ScCH2), 25.1 (q, JCH = 125.6 Hz, CCH3), 4.76 (q, JCH = 116.9 Hz, Si(CH3)3), 2.5 (q, JCH =
117.8 Hz, Si(CH3)2). Anal. Calcd for C24H50N3ScSi3: C, 56.53; H, 9.88; N, 8.24. Found: C,
56.85; H, 9.97; N, 8.02.
Chapter 4
76
Synthesis of [(L3)Sc(CH2SiMe3)(THF)2][B(C6H5)4] (19). A solution of HL3 (47.7 mg,
278 μmol) in THF (1 mL) was added to Sc(CH2SiMe3)3(THF)2 (126 mg, 278 μmol). The
resulting homogeneous solution was added to [PhMe2NH][B(C6H5)4] (123 mg, 278 μmol).
The solution was homogenized by agitation and allowed to stand for about 20 min. n-Hexane
(6 mL) was carefully layered on the top and colorless crystalline material formed upon
standing at room temperature for 2 days. The mother liquor was decanted and the solid was
dried under reduced pressure, yielding the title compound (174 mg, 227 μmol, 82%) as a
white solid. 1H NMR (500 MHz, THF-d8, -50 ºC): δ 7.24 (br, 8H, o-H PhB), 6.85 (t, 8H, JHH
= 7.60 Hz, m-H PhB), 6.72 (t, 4H, JHH = 7.12 Hz, p-H PhB), 3.57 (m, 8H, α-H THF), 2.94 (d,
1H, JHH = 12.0 Hz CCHH), 2.90 (m, 1H, NCHH), 2.80 (s, 3H, NCH3), 2.71 (d, 1H, JHH = 12.0
Hz, CCHH), 2.70 (m, 1H, NCHH), 2.69 (d, 1H, JHH = 12.0 Hz, CCHH), 2.46 (s, 3H, NCH3),
2.44 (m, 1H, NCHH), 2.41 (m, 1H, NCHH), 2.38 (d, 1H, JHH = 12.0 Hz, CCHH), 2.11 (s, 3H,
NCH3), 1.72 (m, 8H, β-H THF), 0.75 (s, 3H, CCH3), -0.07 (s, 9H, Si(CH3)3), -0.74 (d, 1H,
JHH = 11.8 Hz, ScCHH), -0.79 (d, 1H, JHH = 11.8 Hz, ScCHH). 13C NMR (125.7 MHz,
THF-d8, -50 ºC): δ 166.4 (q, JBC = 49.9 Hz, ipso-C PhB), 138.0 (d, JCH = 151.4 Hz, o-C PhB),
126.9 (d, JCH = 152.5 Hz, m-C PhB), 123.1 (d, JCH = 154.7 Hz, p-C PhB), 79.3 (t, JCH = 135.0
Hz, CCH2), 69.2 (t, JCH = 146.2 Hz, α-C THF), 59.0 (t, JCH = 135.7 Hz, NCH2), 58.8 (t, JCH =
133.7 Hz, NCH2), 57.8 (s, CCH3), 52.2 (q, JCH = 137.7 Hz, NCH3), 50.8 (q, JCH = 136.7 Hz,
NCH3), 36.6 (q, JCH = 130.7 Hz, NCH3), 34.0 (t, JCH = 99.2 Hz, ScCH2), 27.4 (t, JCH =132.1
Hz, β-C THF), 20.0 (q, JCH = 126.3 Hz, CCH3), 4.8 (q, JCH = 116.8 Hz, Si(CH3)3). Anal.
Calcd for C45H67BN3O2ScSi: C, 70.57; H, 8.82; N, 5.49. Found: C, 70.35; H, 8.81; N, 5.09.
Synthesis of [(L4)Sc(CH2SiMe3)(THF)2][B(C6H5)4] (20). THF (3 mL) was added to a
mixture of 15 (85.3 mg, 147 μmol) and [PhMe2NH][B(C6H5)4] (64.7 mg, 147 μmol). The
solution was homogenized by agitation and allowed to stand for about 20 min. Toluene (1 mL)
was added to the mixture to form white precipitate and more THF was added to just dissolve
the precipitate. Upon cooling to -30 °C, colorless crystalline material formed. The mother
liquor was decanted and the solid was dried under reduced pressure yielding the titled
compound as a white solid (87.0 mg, 98.2 μmol, 67%). 1H NMR (500 MHz, THF-d8, -50 ºC):
δ 7.56 (d, 2H, JHH = 7.26 Hz, o-H PhSi), 7.32 (br, 11H, o-H PhB, m-H PhSi, p-H PhSi
overlap), 6.91 (t, 8H, JHH = 7.40 Hz, m-H PhB), 6.78 (t, 4H, JHH = 7.14 Hz, p-H PhB), 3.57 (m,
8H, α-H THF), 3.01 (d, 1H, JHH = 12.0 Hz CCHH), 2.89 (m, 1H, NCHH), 2.70 (d, 1H, JHH =
12.2 Hz, CCHH), 2.64 (m, 1H, NCHH), 2.59 (s, 3H, NCH3), 2.58 (d, 1H, JHH = 12.0 Hz,
CCHH), 2.43 (d, 1H, JHH = 12.2 Hz, CCHH), 2.42 (m, 1H, NCHH), 2.28 (m, 1H, NCHH),
2.19 (s, 3H, NCH3), 1.74 (m, 8H, β-H THF), 0.68 (s, 3H, CCH3), 0.38 (s, 3H, SiCH3), 0.34 (s,
3H, SiCH3), -0.08 (s, 9H, Si(CH3)3), -0.18 (d, 1H, JHH = 11.2 Hz, ScCHH), -0.29 (d, 1H, JHH =
11.2 Hz, ScCHH). 13C NMR (125.7 MHz, THF-d8, -50 ºC): δ 166.4 (q, JBC = 46.5 Hz, ipso-C
PhB), 148.1 (s, ipso-C PhSi), 138.0 (d, JCH = 153.7 Hz, o-C PhB), 134.8 (d, JCH = 154.3 Hz,
o-C PhSi), 129.8 (d, JCH = 158.4 Hz, p-H PhSi), 129.5 (d, JCH = 157.1 Hz, m-H PhSi),
127.0 (d, JCH = 153.2 Hz, m-H PhB), 123.2 (d, JCH = 156.5 Hz, p-H PhB), 82.3 (t, JCH = 136.6
Hz, CCH2), 82.1 (t, JCH = 139.1 Hz, CCH2), 69.2 (t, JCH = 145.0 Hz, α-C THF), 59.5 (t, JCH =
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
77
138.5 Hz, NCH2), 59.1 (t, JCH = 139.2 Hz, NCH2), 57.6 (s, CCH3), 53.6 (q, JCH = 138.2 Hz,
NCH3), 51.3 (q, JCH = 136.7 Hz, NCH3), 40.2 (t, JCH = 92.7 Hz, ScCH2), 27.4 (t, JCH =131.8
Hz, β-C THF), 25.5 (q, JCH = 127.4 Hz, CCH3), 5.4 (q, JCH = 117.4 Hz, SiCH3), 5.2 (q, JCH =
116.7 Hz, Si(CH3)3), 5.0 (q, JCH = 115.5 Hz, SiCH3). Anal. Calcd for C52H75BN3O2ScSi2: C,
70.48; H, 8.53; N, 4.74. Found: C, 70.70; H, 8.80; N, 4.38.
Synthesis of {[CH2CH2CH2(μ-N)-1,4,6-trimethyl-1,4-diazepine]Sc(CH2SiMe3)}2 (21).
Compound 17 (170 mg, 0.28 mmol) was dissolved in toluene (30 mL) and the resulting
solution was exposed to ethylene (1 bar) with vigorous stirring for 3 h at room temperature.
Then all the volatiles were removed under reduced pressure and the residue was purified by
crystallization from a toluene/pentane mixture to give the title compound (134 mg, 0.20
mmol, 71%) as colorless crystals. 1H NMR (500MHz, C6D6): δ 4.42 (m, 2H, NCH2), 3.53 (m,
2H, NCH2), 2.83 (m, 2H, CH2CH2CH2), 2.76 (m, 2H, NCH2), 2.70 (m, 2H, NCH2), 2.59 (m,
2H, NCH2), 2.52 (m, 2H, NCH2), 2.51 (m, 2H, NCH2), 2.32 (s, 6H, NCH3), 2.00 (s, 6H,
NCH3), 1.80 (m, 2H, NCH2), 1.73 (m, 2H, NCH2), 1.71 (m, 2H, NCH2), 1.70 (m, 2H, NCH2),
1.12 (s, 6H, CCH3), 0.93 (m, 2H, NCH2Sc), 0.76 (m, 2H, NCH2Sc), 0.41 (s, 18H, Si(CH3)3),
-0.43 (d, 2H, JHH = 10.9 Hz, ScCH2SiMe3), -0.70 (d, 2H, JHH = 10.9 Hz, ScCH2SiMe3). 13C
NMR (125.7MHz, C6D6): δ 77.5 (t, JCH = 133.6 Hz, NCH2), 64.3 (t, JCH = 136.5 Hz, NCH2),
61.7 (S, CCH3), 61.0 (t, JCH = 135.3 Hz, NCH2), 56.0 (t, JCH = 139.5 Hz, NCH2), 50.9 (q,
JCH = 135.7 Hz, NCH3), 50.2 (q, JCH = 135.7 Hz, NCH3), 47.9 (t, JCH = 116.5 Hz, NCH2Sc),
46.5 (t, JCH = 129.7 Hz, NCH2), 33.6 (t, JCH = 122.4 Hz, CH2CH2CH2), 32.1 (t, JCH = 99.0
Hz, ScCH2), 22.5 (q, JCH = 126.0 Hz, CCH3), 4.9 (q, JCH = 116.0 Hz, Si(CH3)3). Anal. Calcd
for C30H68N6Sc2Si2: C, 54.68; H, 10.40; N, 12.75. Found: C, 54.36; H, 10.37; N, 12.56.
NMR Scale Reaction of 1 Equiv of HL4 with Y(CH2Ph)3(THF)3. A solution of ligand
precursor HL4 (26.8 mg, 92 μmol) in benzene (0.5 mL) was added to Y(CH2Ph)3(THF)3
(53.2 mg, 92 μmol) and the resulting solution was transferred to an NMR tube equipped with
a Teflon (Young) valve. All the volatiles were removed under reduced pressure and the
residue was dissolved in C6D6 (0.5 mL). The solution was analyzed by NMR spectrometry
and the NMR spectra indicated that the product was (L4)Y(CH2Ph)2(THF). 1H NMR (400
MHz, C6D6, 50 ˚C) δ: 7.85 (d, 2H, JHH = 7.0 Hz, o-H PhSi), 7.35 (t, 2H, JHH = 7.5 Hz, m-H
PhSi), 7.85 (t, 1H, JHH = 7.2 Hz, p-H PhSi), 7.05 (m, 8H, o-H and m-H PhCH2Y), 6.55 (br, 2H,
p-H PhCH2Y), 3.52 (m, 4H, α-H THF), 2.56 (m, 2H, NCH2), 2.52 (d, 2H, JHH = 12.0 Hz,
CCH2), 2.14 (s, 6H, NCH3), 2.07 (br, 4H, YCH2), 1.88 (d, 2H, JHH = 12.0 Hz, CCH2), 1.65 (m,
2H, NCH2), 1.31 (m, 4H, β-H THF), 0.75 (s, 3H, CCH3), 0.62 (s, 6H, Si(CH3)2). 13C{1H}
(100.6 MHz, C6D6, 25 ˚C) δ: 155.7 (ipso-C Ph), 147.8 (ipso-C Ph), 133.9 (o-C Ph), 128.7
(o-C Ph), 128.2(m-C Ph), 128.1 (m-C Ph), 123.4 (p-C Ph), 115.9 (p-C Ph), 80.7 (CCH2), 70.3
(α-C THF), 57.7 (NCH2), 57.6 (CCH3), 53.5 (d, JYC = 30.8 Hz, YCH2), 49.6 (NCH3), 25.3
(CCH3), 25.1 (β-C THF), 4.0 (Si(CH3)2). To this NMR tube, another equiv of HL4 (26.8 mg,
92 μmol) in benzene (0.3 mL) was added and the tube was allowed to stand at room
temperature overnight. It was analyzed by NMR spectrometry and the 1H NMR spectrum
Chapter 4
78
indicated quantitative formation of compound 22.
Synthesis of (L4)Y{PhMe2SiNC(Me)(CH2NMe)[CH2N(Me)CH=CH2]} (22). A solution
of ligand precursor HL4 (0.408 g, 1.4 mmol) in toluene (30 mL) was added to
Y(CH2Ph)3(THF)3 (0.405 g, 0.7 mmol) at room temperature and the resulting solution was
stirred overnight. All the volatiles were removed under reduced pressure and the residue was
purified by crystallization from toluene/hexane, yielding the title product (0.348 g, 0.52
mmol, 74%) as colorless crystals. Crystals suitable for single-crystal X-ray diffraction were
grown by slow evaporation of a concentrated solution of 22 in benzene. 1H NMR (500 MHz,
C6D6, 25 ̊ C): δ 7.99 (d, 2H, JHH = 6.9 Hz, o-H Ph), 7.94 (d, 2H, JHH = 6.9 Hz, o-H Ph), 7.38 (t,
2H, JHH = 7.2 Hz, m-H Ph), 7.36 (t, 2H, JCH = 7.2 Hz, m-H Ph), 7.25 (br, 2H, p-H Ph), 6.39
(dd, 1H, JHH = 8.6 Hz, JHH = 15.8 Hz, CH=CH2), 3.95 (d, 1H, JHH = 8.6 Hz, CH=CH2), 3.86
(dd, 1H, JHH = 15.8 Hz, CH=CH2), 3.75 (d, 1H, JHH = 9.9 Hz, CCH2), 3.21 (s, 3H, NCH3),
2.95 (d, 1H, JHH = 10.0 Hz, CCH2), 2.77 (m, 2H, xx), 2.72 (d, 1H, JHH = 11.8 Hz, CCH2), 2.39
(d, 1H, JHH = 12.4 Hz, CCH2), 2.36 (m, 1H, NCH2), 2.31 (s, 3H, NCH3), 2.28 (m, 1H, NCH2),
2.23 (s, 3H, NCH3), 2.11 (s, 3H, NCH3), 1.91 (d, 1H, JHH = 12.4 Hz, CCH2), 1.72 (d, 1H, JHH
= 11.8 Hz, CCH2), 1.55 (m, 1H, NCH2), 1.49 (m, 1H, NCH2), 1.22(s, 3H, CCH3), 0.89 (s, 3H,
Si(CH3)2), 0.80 (s, 3H, CCH3), 0.79 (s, 3H, Si(CH3)2), 0.78 (s, 3H, Si(CH3)2), 0.73 (s, 3H,
Si(CH3)2). 13C NMR (125.7 Hz, C6D6, 25 ̊ C): δ 150.9 (d, JCH = 170.1 Hz, CH=CH2), 148.8 (s,
ipso-C Ph), 134.2 (dt, JCH = 155.0 Hz, JCH = 7.2 Hz, m-C Ph), 127.8 (d, JCH = 158.3 Hz, o-C
Ph), 127.7 (d, JCH = 158.2 Hz, p-C Ph), 91.4 (t, JCH = 161.1 Hz, CH=CH2), 83.5 (t, JCH =
139.1 Hz, CCH2), 79.0 (t, JCH = 133.8 Hz, CCH2), 77.4 (t, JCH = 128.3 Hz, CCH2), 75.9 (t, JCH
= 136.5 Hz, CCH2), 58.6 (t, JCH = 136.8 Hz, NCH2), 56.5 (s, CCH3), 55.7 (t, JCH = 137.9 Hz,
NCH2), 55.3 (CCH3), 49.0(q, JCH = 135.2 Hz, NCH3), 48.6 (q, JCH = 135.7 Hz, NCH3), 44.4
(q, JCH = 127.1 Hz, NCH3), 42.3 (q, JCH = 136.9 Hz, NCH3), 29.6 (q, JCH = 125.9 Hz, CCH3),
26.7 (q, JCH = 124.7 Hz, CCH3), 5.0 (q, JCH = 117.6 Hz, Si(CH3)2), 4.8 (q, JCH = 116.6 Hz,
Si(CH3)2), 4.3 (q, JCH = 116.6 Hz, Si(CH3)2), 2.6 (q, JCH = 116.9 Hz, Si(CH3)2). Anal. Calcd
for C32H55N6Si2Y: C, 57.46; H, 8.29; N, 12.56. Found: C, 57.33; H, 8.32; N, 12.28.
Synthesis of (L4)Y[CH2=CHN(Me)C(Me)(CH2NMe)2] (23). A solution of ligand
precursor HL3 (0.103 g, 0.6 mmol) in toluene (10 mL) was added to 16 (0.376 g, 0.6 mmol)
and the resulting solution was stirred at 50 ̊ C for 4 h. All of the volatiles were removed under
reduced pressure and the residue was purified by crystallization from a toluene/n-hexane
mixture, yielding the title compound (0.258 g, 0.47 mmol, 78%) as a colorless solid. 1H NMR
(500 MHz, C6D6, 25 C): 7.98 (d, 2H, JHH = 6.9 Hz, o-H Ph), 7.39 (t, 2H, JHH = 7.2 Hz, m-H
Ph), 7.26 (t, 1H, JHH = 7.3 Hz, p-H Ph), 6.52 (dd, 1H, JHH = 15.6 Hz, JHH = 9.0 Hz,
NCH=CH2), 4.14 (d, 1H, JHH = 9.0 Hz, NCH=CHH), 4.05 (d, 1H, JHH = 15.6 Hz,
NCH=CHH), 3.61 (d, 1H, JHH = 11.9 Hz, CCH2), 3.56 (d, 1H, JHH = 11.7 Hz, CCH2), 3.26 (s,
3H, NCH3), 3.25 (d, 1H, JHH = 11.9 Hz, CCH2) , 3.24 (s, 3H, NCH3), 3.11 (d, 1H, JHH = 11.7
Hz, CCH2), 2.53 (d, 1H, JHH = 12.3 Hz, CCH2), 2.51 (m, 1H, NCH2), 2.49 (d, 1H, JHH = 12.2
CCH2), 2.26 (s, 3H, NCH3), 2.19 (s, 3H, NCH3), 2.16 (m, 1H, NCH2), 2.11(s, 3H, NCH3),
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
79
1.93 (d, 1H, JHH = 12.2 Hz, CCH2), 1.91 (d, 1H, JHH = 11.9 Hz, CCH2), 1.64 (m, 1H, NCH2),
1.59 (m, 1H, NCH2), 1.04 (s, 3H, CCH3), 0.78 (s, 3H, CCH3), 0.76 (s, 6H, Si(CH3)2). 13C
NMR (125.7 MHz, C6D6, 25 C): 148.2 (s, ipso-C Ph), 144.5 (d, JCH = 175.0 Hz,
NCH=CH2), 134.0 (d, JCH = 154.6 Hz, o-C Ph), 128.3 (d, JCH = 157.2 Hz, m-C Ph), 127.9 (d,
JCH = 159.8 Hz, p-C Ph), 93.7 (t, JCH = 157.5 Hz, NCH=CH2), 80.7 (t, JCH = 139.8 Hz, CCH2),
79.4 (t, JCH = 143.2 Hz, CCH2), 69.8 (t, JCH = 125.3 Hz, CCH2), 69.2 (t, JCH = 130.3 Hz,
CCH2), 64.2 (s, CCH3), 57.1 (t, JCH = 134.7 Hz, NCH2), 56.1 (t, JCH = 127.1 Hz, NCH2), 55.2
(s, CCH3), 49.2 (q, JCH = 137.3 Hz, NCH3), 48.8 (q, JCH = 136.0 Hz, NCH3), 43.7 (q, JCH =
128.2 Hz, NCH3), 43.6 (q, JCH = 128.2 Hz, NCH3), 31.8 (q, JCH = 136.4 Hz, NCH3), 26.0 (q,
JCH = 125.0 Hz, CCH3), 20.2 (q, JCH = 126.1 Hz, CCH3), 1.83 (q, JCH = 117.1 Hz, Si(CH3)2).
Anal. Calcd. For C25H47N6SiY: C, 54.73; H, 8.63; N, 15.32. Found: C, 54.08; H, 8.64; N,
14.82. The assignment of NMR resonances was aided by COSY and HSQC experiments.
Synthesis of (L3)(L19)YCH2SiMe3 (24). A solution of L2 (0.356 g, 1.45 mmol) in toluene
(20 mL) was added to Y(CH2SiMe3)3(THF)3 (0.718 g, 1.45 mmol) and the resulting mixture
was stirred at room temperature for 20 min. Then a solution of ligand precursor HL3 (0.249 g,
1.45 mmol) in toluene (2 mL) was added. The mixture was stirred for another 10 min and all
the volatiles were removed under reduced pressure. The residue was dissolved in toluene (1
mL) and pentane was added until a precipitate began to form. Upon cooling to -30 ˚C
overnight, a crystalline material formed, including material suitable for single-crystal X-ray
diffraction. The mother liquor was decanted and the solid was dried under reduced pressure,
yielding the title compound (0.808 g, 1.19 mmol, 82%) as a colorless crystalline solid. 1H
NMR (500 MHz, C7D8, -30˚C) δ: 7.74 (br, 1H, p-H Ph), 7.31 (br, 2H, m-H Ph), 7.12 (d, 2H,
JHH = 8.4 Hz, o-H Ph), 4.39 (dd, 1H, JHH = 11.5 Hz, JHH = 2.8 Hz, PhCH), 3.88 (d, 1H, JHH =
11.6 Hz, CCH2), 3.46 (t, 1H, JHH = 11.6 Hz, NCH2), 2.99 (s, 3H, NCH3), 2.97 (d, 1H, JHH =
11.6 Hz, CCH2), 2.76 (d, 1H, JHH = 10.8 Hz, CCH2), 2.52 (d, 1H, JHH = 11.6 Hz, CCH2), 2.33
(d, 1H, JHH = 12.2 Hz, CCH2), 2.32 (m, 1H, NCH2), 2.30 (s, 3H, NCH3), 2.20 (s, 3H, NCH3),
2.19 (d, 1H, JHH = 10.0 Hz, NCH2), 2.15 (m, 1H, NCH2), 1.71 (m, 1H, NCH2), 2.05 (s, 3H,
NCH3), 2.04 (s, 3H, NCH3), 2.01 (m, 2H, Me2SiCH2), 1.94 (m, 1H, NCH2), 1.83 (d, 1H, JHH
= 11.6 Hz, NCH2), 1.80 (d, 1H, JHH = 12.2 Hz, CCH2), 1.69 (d, 1H, JHH = 10.8 Hz, CCH2),
1.63 (d, 1H, JHH = 11.6 Hz, CCH2), 1.50 (d, 1H, JHH = 10.0 Hz, NCH2), 1.26 (s, 3H, CCH3),
0.56 (s, 9H, Si(CH3)3), 0.48 (s, 3H, CCH3), 0.08 (s, 9H, Si(CH3)3), -0.04 (d, 1H, JHH = 10.3
Hz, YCH2), -1.06 (d, 1H, JHH = 10.3 Hz, YCH2). 13C{1H} NMR (125.7 MHz, C7D8, -30 ̊ C) δ:
156.9 (ipso-C Ph), 78.7 (CCH2), 75.5 (CCH2), 67.2 (CCH2), 63.7 (CCH2), 59.9 (PhCH), 58.4
(CCH3), 57.7 (NCH2), 57.3 (NCH2), 57.3 (CCH3), 55.2 (NCH2), 50.7 (NCH3), 50.4 (NCH3),
50.2 (NCH2), 48.1 (NCH3), 46.7 (NCH3), 34.5 (NCH3), 27.7 (CCH3), 27.6 (Me3SiCH2), 23.8
(CCH3), 22.5 (d, JYC = 40.7 Hz, YCH2), 5.9 (Si(CH3)3), -0.7 (Si(CH3)3). The o-C, m-C, p-C
resonances are obscured by the solvent peaks. Anal. Calcd. for C32H65N6Si2Y: C, 56.61, H,
9.65, N, 12.38; Found: C, 56.82, H, 9.79, N, 12.31.
Thermolysis of yttrium monoalkyl compound 24. C6D6 (0.5 mL) was added to 24 (27.2
Chapter 4
80
mg, 40 μmol) and the resulting solution was transferred to an NMR tube equipped with a
Teflon Young valve. The NMR tube was heated for 6 h in the oven preheated to 80 ˚C and
then analyzed by NMR spectrometry. NMR analysis indicates that two organometallic
compounds (molar ratio 53/47), each bearing a vinyl group, had formed. The NMR spectra of
the reaction mixture were complicated by severe signal overlap. Only well-resolved
resonances are listed. 1H NMR (500 MHz, C6D6, 23 ˚C): δ 6.55 (dd, JHH = 15.7 Hz, JHH =
9.0 Hz, CH=CH2), 4.42 (dd, JHH = 12.2 Hz, JHH = 3.4 Hz, PhCH), 4.17 (d, JHH = 9.0 Hz,
CH=CH2), 4.15 (d, JHH = 9.0 Hz, CH=CH2) 4.08 (d, JHH = 15.7 Hz, CH=CH2), 4.06 (d, JHH =
15.7 Hz, CH=CH2), 3.44 (s, NCH3), 3.24 (s, NCH3). {1H}13C NMR (125.7 MHz, C6D6, 23 ̊ C)
δ: 155.8 (ipso-C Ph), 155.7 (ipso-C Ph), 144.7 (NCH=CH2), 144.6 (NCH=CH2), 93.8
(NCH=CH2), 93.4 (NCH=CH2), 79.7 (CCH2), 78.9 (CCH2), 78.4 (CCH2), 77.2 (CCH2), 70.4
(CCH2), 69.7 (CCH2), 60.6 (PhCH), 57.4 (NCH2), 56.8 (NCH2), 56.5 (NCH2), 55.7 (NCH2),
49.6 (NCH3), 49.2 (NCH3), 49.1 (NCH3), 48.9 (NCH3), 48.8 (NCH3), 48.5 (NCH3), 45.0
(NCH3), 44.8 (NCH3), 44.4 (NCH3), 44.3 (NCH3).
Synthesis of (L3)Sc[CH2=CHN(Me)C(Me)(CH2NMe)2] (25). A solution of ligand
precursor HL3 (0.268 g, 1.56 mmol) in toluene (20 mL) was added to Sc(CH2SiMe3)3(THF)2
(0.353 g, 0.78 mmol) at room temperature and the resulting mixture was stirred overnight.
All the volatiles were removed under reduced pressure and the residue was dissolved in
toluene (1 mL) and hexane was added until precipitate formed. Upon cooling to -30 ˚C,
crystalline material formed, including crystals suitable for single-crystal X-ray diffraction.
The mother liquor was decanted and the solid was dried under reduced pressure, yielding the
title compound (0.233 g, 0.56 mmol, 72%) as a colorless solid. 1H NMR (500 MHz,
toluene-d8, 25 ˚C): δ 6.45 (dd, 1H, JHH = 8.9 Hz, JHH = 15.9 Hz, CH=CH2), 4.17 (d, 1H, JHH =
8.9 Hz, CH=CH2), 4.09 (d, 1H, JHH = 15.9 Hz, CH=CH2), 3.57 (d, 1H, JHH = 11.5 Hz, CCH2),
3.53 (d, 1H, JHH = 11.4 Hz, CCH2), 3.23 (dd, 1H, JHH = 11.4 Hz, JHH = 1.8 Hz, NCH2), 3.16 (s,
3H, NCH3), 3.15 (s, 3H, NCH3), 3.12 (dd, 1H, JHH = 11.4 Hz, JHH = 1.8 Hz, NCH2), 3.09 (s,
3H, NCH3), 2.76 (dt, 1H, JHH = 11.7 Hz, JHH = 2.2 Hz, NCH2), 2.69 (dt, 1H, JHH = 11.9 Hz,
JHH = 2.2 Hz, NCH2), 2.25 (m, 1H, NCH2), 2.24 (s, 3H, NCH3), 2.22 (s, 3H, NCH3), 2.16 (s,
3H, NCH3), 2.00 (d, 1H, JHH = 11.9 Hz, NCH2), 1.94 (d, 1H, JHH = 11.7 Hz, NCH2), 1.83 (m,
1H, NCH2), 1.75 (m, 1H, NCH2), 1.02 (s, 3H, CCH3), 0.75 (s, 3H, CCH3). 13C NMR (125.7
MHz, C6D6, 25 ˚C): δ 144.9 (d, JCH = 170.0 Hz, NCH=CH2), 94.1 (t, JCH = 157.4 Hz,
NCH=CH2), 75.9 (t, JCH = 134.7 Hz, CCH2), 74.8 (t, JCH = 134.7 Hz, CCH2), 69.6 (t, JCH =
130.5 Hz, amido-NCH2C), 68.9 (t, JCH = 130.5 Hz, amido-NCH2C), 64.7 (s, CCH3), 57.7 (t,
JCH = 139.6 Hz, NCH2), 56.6 (t, JCH = 139.6 Hz, NCH2), 55.6 (s, CCH3), 49.8 (q, JCH = 135.9
Hz, NCH3), 49.3 (q, JCH = 135.9 Hz, NCH3), 43.7 (q, JCH = 127.9 Hz, amido-NCH3), 43.6 (q,
JCH = 127.9 Hz, amido-NCH3), 33.6 (q, JCH = 128.6 Hz, amido-NCH3), 32.0 (q, JCH = 135.9
Hz, NCH3), 20.1 (q, JCH = 118.1 Hz, CCH3), 18.8 (q, JCH = 118.1 Hz, CCH3). Anal. Calcd for
C18H39N6Sc: C, 56.23; H, 10.22; N, 21.86. Found: C, 56.01; H, 10.14; N, 21.00.
General procedure for ethylene polymerization. In a typical experiment, solutions were
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
81
prepared in a dry-box of the complexes 14, 15, 18 (10 μmol) and of [HNMe2Ph][B(C6F5)4]
(10 μmol), each in 5 ml of toluene in separate vials sealed with a serum cap. The autoclave
was charged with 200 ml of toluene (after injection of (co)catalyst solutions and rinsing the
vials, the total volume of toluene was 250 ml), equilibrated at the 50 °C, and pressurized with
ethylene (5 bar). The solution of [HNMe2Ph][B(C6F5)4] was injected first into the reactor and
the reaction was started by subsequently injecting the solution of the catalyst precursors. The
ethylene pressure was kept within 0.1 bar of the initial pressure during the reaction by
replenishing flow. The polymerization was run for 10 min. The obtained polymer was rinsed
with ethanol and dried in a vacuum oven (70 °C).
Structure Determinations of Compound 14-17, and 21-25. These measurements were
performed according to the procedure described for complex 1 in Chapter 2. Crystallographic
data and details of the data collections and structure refinements are listed in Table 4.8 (for
14-16), Table 4.9 (for 17, 21, and 22), and 4.10 (23-25).
Chapter 4
82
Table 4.8. Crystal Data and Collection Parameters of Complexes 14-16.
Compound 14 15 16
Formula C21H50N3OScSi2 C28H58N3OScSi3 C28H58N3OSi3Y
Fw 461.77 581.99 625.95
cryst color, habit colorless, block colorless, block colorless, block
cryst size (mm) 0.45 0.21 0.12 0.45 0.41 0.36 0.37 0.22 0.11
cryst syst triclinic triclinic triclinic
space group P-1 P-1 P-1
a (Å) 8.883(2) 9.4978(4) 9.5382(7)
b (Å) 9.665(2) 12.0208(5) 12.1759(9)
c (Å) 17.508(3) 15.6141(7) 15.6951(11)
(deg) 98.910(3) 79.1238(7) 79.3149(12)
(deg) 102.205(3) 79.1083(7) 79.0368(12)
(deg) 105.553(3) 79.6515(7) 81.0115(12)
V (Å3) 1379.2(5) 1699.85(13) 1744.6(2)
Z 2 2 2
calc, g.cm-3 1.112 1.137 1.192
µ(Mo Kα), cm-1 3.69 3.46 17.97
F(000), electrons 508 636 672
θ range (deg) 2.77, 25.03 2.60, 28.28 2.68, 27.10
Index range (h, k, l) ±10, -11:10, ±20 ±12, -16:15, ±20 ±12, ±15, -20:18
Min and max transm 0.8270, 0.9567 0.8451, 0.8829 0.5342, 0.8206
no. of reflns collected 8929 15551 14697
no. of reflns collected 4738 8116 7465
no. of reflns with F0 ≥ 4 σ (F0) 3343 6938 5925
wR(F2) 0.1569 0.0947 0.0908
R(F) 0.0587 0.0360 0.0395
weighting a, b 0.0776, 0 0.0529, 0.39 0.0471, 0
Goof 1.059 1.056 0.991
params refined 263 557 557
min, max resid dens -0.41, 0.48(9) -0.19, 0.49(6) 0.32, 0.65(8)
T (K) 100(1) 100(1) 100(1)
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
83
Table 4.9. Crystal Data and Collection Parameters of Complexes 17, 21, and 22.
Compound 17 21 22
Formula C26H60N6Sc2Si2 C28H58N3OScSi3 C28H58N3OSi3Y
Fw 602.89 581.99 625.95
cryst color, habit colorless, block colorless, block colorless, block
cryst size (mm) 0.44 0.37 0.19 0.45 0.41 0.36 0.37 0.22 0.11
cryst syst monoclinic triclinic triclinic
space group P21/n P-1 P-1
a (Å) 13.316(1) 9.4978(4) 9.5382(7)
b (Å) 16.815(1) 12.0208(5) 12.1759(9)
c (Å) 16.211(1) 15.6141(7) 15.6951(11)
(deg) 79.1238(7) 79.3149(12)
(deg) 102.205(3) 79.1083(7) 79.0368(12)
(deg) 110.118(1) 79.6515(7) 81.0115(12)
V (Å3) 3408.3(4) 1699.85(13) 1744.6(2)
Z 4 2 2
calc, g.cm-3 1.175 1.137 1.192
µ(Mo Kα), cm-1 4.92 3.46 17.97
F(000), electrons 1312 636 672
θ range (deg) 2.42, 27.10 2.60, 28.28 2.68, 27.10
Index range (h, k, l) -17:16, ±21, ±20 ±12, -16:15, ±20 ±12, ±15, -20:18
Min and max transm 0.7921, 0.9107 0.8451, 0.8829 0.5342, 0.8206
no. of reflns collected 28317 15551 14697
no. of reflns collected 7464 8116 7465
no. of reflns with F0 ≥ 4 σ (F0) 5637 6938 5925
wR(F2) 0.1070 0.0947 0.0908
R(F) 0.0451 0.0360 0.0395
weighting a, b 0.0552, 0.256 0.0529, 0.39 0.0471, 0
Goof 1.037 1.056 0.991
params refined 565 557 557
min, max resid dens -0.34, 0.50(8) -0.19, 0.49(6) 0.32, 0.65(8)
T (K) 100(1) 100(1) 100(1)
Chapter 4
84
Table 4.10. Crystal Data and Collection Parameters of Complexes 23-25.
Compound 23 24 25
Formula C26H60N6Sc2Si2 C28H58N3OScSi3 C28H58N3OSi3Y
Fw 602.89 581.99 625.95
cryst color, habit colorless, block colorless, block colorless, block
cryst size (mm) 0.44 0.37 0.19 0.45 0.41 0.36 0.37 0.22 0.11
cryst syst monoclinic triclinic triclinic
space group P21/n P-1 P-1
a (Å) 13.316(1) 9.4978(4) 9.5382(7)
b (Å) 16.815(1) 12.0208(5) 12.1759(9)
c (Å) 16.211(1) 15.6141(7) 15.6951(11)
(deg) 79.1238(7) 79.3149(12)
(deg) 102.205(3) 79.1083(7) 79.0368(12)
(deg) 110.118(1) 79.6515(7) 81.0115(12)
V (Å3) 3408.3(4) 1699.85(13) 1744.6(2)
Z 4 2 2
calc, g.cm-3 1.175 1.137 1.192
µ(Mo Kα), cm-1 4.92 3.46 17.97
F(000), electrons 1312 636 672
θ range (deg) 2.42, 27.10 2.60, 28.28 2.68, 27.10
Index range (h, k, l) -17:16, ±21, ±20 ±12, -16:15, ±20 ±12, ±15, -20:18
Min and max transm 0.7921, 0.9107 0.8451, 0.8829 0.5342, 0.8206
no. of reflns collected 28317 15551 14697
no. of reflns collected 7464 8116 7465
no. of reflns with F0 ≥ 4 σ (F0) 5637 6938 5925
wR(F2) 0.1070 0.0947 0.0908
R(F) 0.0451 0.0360 0.0395
weighting a, b 0.0552, 0.256 0.0529, 0.39 0.0471, 0
Goof 1.037 1.056 0.991
params refined 565 557 557
min, max resid dens -0.34, 0.50(8) -0.19, 0.49(6) 0.32, 0.65(8)
T (K) 100(1) 100(1) 100(1)
Scandium and Yttrium Alkyl Complexes with the fac-κ3 1,4-Diazepan-6-amido Ligands
85
4.6 References:
1. For reviews, see (a) Edelmann, F. T. Comprehensive Organometallic Chemistry III, 2007, 4,
1. (b) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. Rev. 2006, 106, 2404. (c)
Arndt, S.; Okuda, J. Adv. Synth. Catal. 2005, 347, 339.
2. Cp-based ligands: (a) Luo, Y.; Baldamus, J.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 13910. (b)
Li, X.; Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 962. (c) Cui, D.; Nishiura, M.;
Hou, Z., Macromolecules 2005, 38, 4089. (d) Li, X.; Hou, Z. Macromolecules 2005, 38,
6767.
3. TACN-based ligands: (a) Hajela, S.; Schaefer , W. P.; Bercaw, J. E. J. Organomet. Chem.
1997, 532, 45. (b) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H.
Chem. Commun. 2001, 637. (c) Lawrence, S. C.; Ward, B. D.; Dubberley, S. R.; Kozak, C.
M.; Mountford, P. Chem. Commun. 2003, 2880. (d) Tredget, C. S.; Lawrence, S. C.; Ward, B.
D.; Howe, R. G.; Cowley, A. R.; Mountford, P. Organometallics 2005, 24, 3136. (e)
Bambirra, S.; Meetsma, A.; Hessen, B.; Bruins, A. P. Organometallics 2006, 25, 3486. (f)
Bambirra, S.; van Leusen, D.; Tazelaar, C. G. J.; Meetsma, A.; Hessen, B. Organometallics
2007, 26, 1014.
4. -diketiminate ligands: (a) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc. 2002,
124, 2132. (b) Hayes, P. G.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc, 2003, 125, 2132. (c)
Hayes, P. G.; Piers, W. E.; Parvez, M. Chem. Eur. J. 2007, 13, 2632.
5. Amidinate ligands: (a) Hagadorn, J. R.; Arnold, J. Organometallics 1996, 15, 984. (b)
Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2003,
522. (c) Bambirra, S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004,
126, 9182.
6. Other ligands: (a) Long, D. P.; Bianconi, P. A. J. Am. Chem. Soc. 1996, 118, 12453. (b)
Lauterwasser, F.; Hayes, P. G.; Brase, S.; Piers, W. E.; Schafer, L. L. Organometallics 2004,
23, 2234. (c) Ward, B. D.; Bellemin, L. S.;Gade, L. H. Angew. Chem., Int. Ed. 2005, 44,
1668. (d) Tredget, C. S.; Bonnet, F.; Cowley, A. R.; Mountford, P. Chem. Commun. 2005,
3301. (e) Howe, R. G.; Tredget, C. S.; Lawrence, S. C.; Subongkoj, S.; Cowley, A. R.;
Mountford, P. Chem. Commun. 2006, 223. (f) Luo, Y.; Nishiura, M.; Hou, Z. J. Organomet.
Chem. 2007, 692, 536. (g) Lukesova, L.; Ward, B. D.; Bellemin-Laponnaz, S.; Wadepohl, H.;
Gade, L. H. Dalton Transactions 2007, 920.
7. (a) Giesbrecht, G. R.; Shafir, A.; Arnold, J. Chem. Commun. 2000, 2135 (b) Qian, B.;
Henling, L. M.; Peters, J. C. Organometallics 2000, 2805. (c) Schmidt, J. A. R.; Giesbrecht,
G. R.; Cui, C.; Arnold, J. Chem. Commun. 2003, 1025.
8. Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973, 126.
9. Beetstra, D. J; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics 2003, 22, 4372.
Chapter 4
86
10. Bambirra, S.; Boot, S. J.; van. Leusen, D.; Meetsma, A.; Hessen, B. Organometallics 2004,
23, 1891.
11. Shannon, R. D. Acta Crystallogr. Sect. A 1976, 32, 751.
12. For related C-H activation of NMe groups in group 3 metal compounds, see: (a) Booij, M.;
Kiers, N. H.; Meetsma, A.; Teuben, J. H. Organometallics 1989, 8, 2454. (b) Mu, Y.; Piers,
W. E.; MacQuarrie, D. C.; Zaworotko, M. J.; Young, V. G., Jr. Organometallics 1996, 15,
2720. (c) Hayes, P. G.; Piers, W. E.; Lee, L. W. M.; Knight, L. K.; Parvez, M.; Elsegood, M.
J. R.; Clegg, W. Organometallics 2001, 20, 2533.
13. (a) Meyer, N.; Roesky, P. W.; Bambirra, S.; Meetsma, A; Hessen, B.; Saliu, K.; Takats, J.
Organometallics 2008, 27, 1501. (b) Carver, C. T.; Montreal, M. J.; Diaconescu, P. L.
Organometallics 2008, 27, 363. (c) Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics,
2006, 25, 3454.
14. Bambirra, S.; Perazzolo, F.; Boot, S. J.; Sciarone, T. J. J.; Meetsma, A.; Hessen, B.
Orgaometallics 2008, 27, 704.
15. Bambirra, S.; Meetsma, A.; Hessen, B.; Bruins, A. P. Organometallics 2006, 25, 3486.
16. Hong, S.; Marks, T. J. Acc. Chem, Res. 2004, 37. 673.
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
87
Chapter 5 Rare Earth Organometallics with Monoanionic
Tetradentate Ligands Derived from the Me3DAPA Moiety
5.1 Introduction
In Chapter 4, we have shown that the monoanionic tridentate ligands L3 and L4, based on
the 1,4,6-trimethyl-1,4-diazepan-6-amine (Me3DAPA) moiety, are suitable to support both
neutral and cationic scandium and yttrium alkyl complexes. However, these ligands are
susceptible to decomposition through ligand H-abstraction processes by the M-alkyl bond,
especially when the metal center is coordinatively unsaturated; e.g. the methyl group on the
6-amido nitrogen of ligand L3 is metalated by the Sc-alkyl bond in
(L3)Sc(CH2SiMe3)2(THF) when it loses the coordinated THF molecule. Also, the
observation that it was impossible with these tridentate ligands to obtain well-defined
dibenzyl complexes of the rare earth metals in the medium to large ionic size range (e.g. Y
and La), indicated that extension of this ligand moiety with additional donor group is
desirable.
Chart I. Ligands Employed in Chapter.
To overcome such disadvantages of these monoanionic tridentate ligands, we
functionalized the Me3DAPA moiety by incorporating an additional nitrogen donor to form
a series of monoanionic tetradentate ligands (L6, L8, L9, L10, and L12 in Chart I). As such,
they would complement the 1,4,7-triazacyclononane-amide ligands pioneered earlier in our
group.1 For tetradentate monoanionic TACN-amide ligands (XIV and XV in Chapter 1), the
negative charge is exclusively located on the pendent amido nitrogen. On the other hand,
the Me3DAPA derivative ligands can have the negative charge located on different positions,
e.g. the 6-amido nitrogen of the Me3DAPA moiety (L6 and L8), delocalized on the
Chapter 5
88
amidinate NCN moiety (L9 and L10), or the pendent amido nitrogen (L12). This gives us a
toolbox to study the ligand effects in the catalytic processes catalyzed by the complexes
bearing these ligands. The synthesis of the protonated form of these ligands was described
in Chapter 2.
In this chapter, we describe the synthesis and characterization of neutral dibenzyl and
cationic monobenzyl complexes of scandium, yttrium, and lanthanum with ligands L6, L8
and L12, and neutral scandium and yttrium dialkyl complexes with ligand L9 and L10.
5.2 Neutral Rare Earth Metal Dibenzyl Complexes
5.2.1 Synthesis of Me3DAPA-Amine Metal Dibenzyl Complexes (L)M(CH2Ph)2 (L
= L6 and L8; M = Sc, Y, and La)
The rare earth metal tribenzyl compounds M(CH2Ph)3(THF)3 have recently emerged as
convenient organo rare earth metal starting materials, which are readily accessible from the
reaction of rare earth metal trichlorides MX3(THF)n with benzyl potassium.2 The target
dibenzyl complexes (L)M(CH2Ph)2 can be conveniently prepared via toluene elimination
by reaction of the corresponding tribenzyls M(CH2Ph)3(THF)3 with the Me3PADA-Amine
ligand precursor HL6 or HL8 in toluene or THF solvent (Scheme 5.1). These reactions were
seen to be quantitative on NMR-tube scale and on a preparative scale afforded the products
26-31 as crystalline materials after crystallization from toluene/pentane mixtures in 68-80%
isolated yield. Complexes 26-31 are highly air and moisture sensitive, but thermally robust
and can be stored in the solid state or in solution at ambient temperature for a few months
without decomposition.
Scheme 5.1. Synthesis of Dibenzyl Complexes 26-31.
To compare the thermal stability of the dibenzyl complexes with their
trimethylsilylmethyl analogues, the dialkyl complex (L6)Y(CH2SiMe3)2 (32) was
synthesized by reaction of HL6 with Y(CH2SiMe3)2(THF)2 in toluene and isolated (isolated
yield: 72%) as a slightly yellow crystalline solid after crystallization from n-hexane. This
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
89
dialkyl complex in C6D6 gradually decomposes at ambient temperature over a period of
days with release of TMS. The enhanced thermal stability of the dibenzyl complex 27 over
the dialkyl complex 32 might be due to the possibility of multihapto binding of the benzyl
group (see the structure of 27). This phenomenon was earlier observed for the lanthanum
alkyl and benzyl complexes bearing a [Me2TACN-SiMe2-NtBu]- ligand.3
All these dibenzyl complexes were studied by single-crystal X-ray diffraction and their
structures are shown in Figure 5.1, with the geometric data compiled in Table 5.1.
Complexes 26-28 are isomorphous; they crystallize in space group P-1 and the crystals
contain two independent molecules in the asymmetric unit, which do not differ significantly;
per compound, only one of them is explicitly discussed here. Complexes 29-31 are also
isomorphous within their own series; they crystallize in space group Pca21 and the crystals
contain one molecule in the asymmetric unit. For complexes 26-28 (with the (CH2)2 bridge),
the scandium complex 26 contains two η1-bound benzyl groups per molecule with
Sc-CH2-Cipso angles of 116.88(18)º and 112.76(17)º, the yttrium complex 27 contains one
η1- and one η2-bound benzyl group per molecule with Y-CH2-Cipso angles of 109.67(18)º
and 96.60(16)º, respetively, and the lanthanum complex 28 contains two η2-bound benzyl
groups with La-CH2-Cipso angles of 89.4(2)º and 93.8(2)º. This indicates that, for complexes
with the same ancillary ligand, the benzyl groups progressively provide more shielding to
the metal center with increasing metal ion radius. A similar trend is observed for complexes
29-31 (with the SiMe2 bridge): the scandium complex 29 contains one η1- and η2-bound
benzyl group with Sc-CH2-Cipso angles of 127.23(14)º and 101.28(13)º, the yttrium complex
30 contains one η1- and one η3-bound benzyl group with Y-CH2-Cipso angles of 124.20(16)º
and 88.11(14)º, and the lanthanum complex 31 contains one η2- and one η3-bound benzyl
group with La-CH2-Cipso angles of 94.79(17)º and 87.55(18)º, respectively. The η3-bound
benzyl group has a phenyl group that is significantly titled, with the difference of 0.94 Å
between the two Y-Co distances (Y-C(28) = 2.949(2) Å and Y-C(24) = 2.889(2) Å) for 30
and 1.02 Å between the two La-Co distances (La-C(28) = 3.058(3) Å and La-C(24) =
4.074(3) Å) for 31. The greater degree of involvement of the benzyl groups in shielding the
metal for complexes with ligand L8 suggests that L8 provides less steric protection to the
metal than L6. This is corroborated by the geometrical parameters for the two ligands (see
below).
Chapter 5
90
Figure 5.1. Structures of Complexes 26-31. All hydrogen atoms are omitted for clarity and
thermal ellipsoids are drawn at the 50% probability level.
In all these complexes 26-31, the 1,4-diazepan-6-amine moiety of the ligands is facially
coordinated, with the shortest M-N distances to the amide nitrogen (N(13) for 26-28 and
N(3) for 29-31). The geometry around the amide nitrogen atom in 26-28 deviates
26
27
28
29
30
31
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
91
significantly from planarity, as seen by the sum of the angles around the amido nitrogen
ΣN(13) (348.3(2)˚ for 26, 348.37(2)˚ for 27, and 349.4(3)˚ for 28), while the geometry
around the amide nitrogen atom in 29-31 is essentially planar (ΣN(3): 358.03(14)˚ for 29,
359.71(18)˚ for 30, and 360.00(19)˚ for 31). The other two amine nitrogen atoms of the
1,4-diazepan-6-amine moiety in 26-28 bind to the metal center unequally, with the
differences of 0.197, 0.135, and 0.178 Å between the two M-N(amine) distances for 26, 27,
and 28, respectively. The longer M-N(amine) bonds are located approximately trans to one
of the benzyl methylene groups, as seen by the angles N(12)-Sc(1)-C(116) = 176.26˚,
N(12)-Y(1)-C(116) = 175.18˚, and N(11)-La(1)-C(123) = 169.65˚. Similar asymmetries were
observed previously in various triamine-amide rare earth metal alkyl complexes.1b,4 The
corresponding differences in 29-31 are somewhat smaller (max. 0.052 Å for 29).
Table 5.1. The Geometric Data of Complexes 26-31.
26 (M = Sc) 27 (M = Y) 28 (M = La)
M(1)-N(11) 2.382(2) 2.524(2) 2.861(3)
M(1)-N(12) 2.585(2) 2.659(2) 2.683(3)
M(1)-N(13) 2.063(2) 2.217(2) 2.352(3)
M(1)-N(14) 2.362(2) 2.512(2) 2.653(3)
M(1)-C(115) 2.329(3) 2.491(3) 2.735(4)
M(1)-C(116) 3.074(4)
M(1)-C(122) 2.368(3) 2.544(3) 2.654(4)
M(1)-C(123) 3.071(3) 3.097(4)
M(1)-C(115)-C(116) 116.88(18) 109.67(18) 89.4(2)
M(1)-C(122)-C(123) 112.76(17) 96.60(16) 93.8(2)
ΣN(13) 348.3(2) 348.37(2) 349.4(3)
29 (M = Sc) 30 (M = Y) 31 (M = La)
M-N(1) 2.4546(19) 2.6113(19) 2.795(2)
M-N(2) 2.5067(17) 2.6079(18) 2.756(2)
M-N(3) 2.0664(16) 2.2175(18) 2.359(2)
M-N(4) 2.4707(16) 2.5738(19) 2.728(3)
M-C(15) 2.337(2) 2.489(2) 2.663(3)
M-C(16) 3.135(3)
M-C(22) 2.326(2) 2.527(2) 2.756(3)
M-C(23) 2.861(2) 3.043(3)
M-C(28) 2.949(2) 3.059(3)
M-C(15)-C(16) 101.28(13) 124.20(16) 94.79(17)
M-C(22)-C(23) 127.23(14) 88.11(14) 87.55(18)
Chapter 5
92
The effect of the bridge moiety ((CH2)2 or SiMe2) in the Me3DAPA-amide ligands can be
seen in comparing the structures of their complexes of the same metal, e.g. the scandium
complexes 26 and 29. The N(pyrrolidinyl)-Sc-N(amido) ligand “bite” angle for the (CH2)2
bridge in 26 of 76.16(8)˚ is noticeably larger than for the SiMe2 bridge in 29 (68.38(6)˚),
indicating the greater geometry constraint in the latter. The effect of this constraint on the
Sc-N(pyrrolidinyl) bond distance is significant, as this increases from 2.362(2) Å
(Sc(1)-N(14) in 26) to 2.4707(16) Å (Sc-N(4) in 29) upon changing from the (CH2)2 bridge to
SiMe2 bridge. This constraint also makes the ligand L8 (with the SiMe2 bridge) less sterically
demanding, as seen by one η1 and one η2-bound benzyl group in 29 (compared with two
η1-bound benzyl groups in 26). Similar effects can also be observed for the yttrium (27 and
30) and lanthanum (28 and 31) complexes.
These dibenzyl complexes were studied by NMR spectroscopy and their 1H NMR
spectra in C6D6 at ambient temperature reveal an averaged Cs symmetric structure. For
complexes 26-28 (bearing a (CH2)2 bridge), the pendant pyrrolidinyl groups are tightly
bound to the metal centers on the NMR time scale, as the sets of its α- and β-H resonances are
all diastereotopic at ambient temperature. For complexes 29-31 (bearing a SiMe2 bridge), the
pendant pyrrolidinyl groups coordinate to the metal center fluxionally as indicated by the fact
that of the pyrrolidinyl group both the α- and β-H protons show a single resonance at ambient
temperature. Low-temperature 1H NMR studies on 29-31 were performed in toluene-d8, and
decoalescence of the α-H resonance was observed at -35 ˚C for the scandium complex 29 and
at 0 ˚C for the yttrium complex 30. For the lanthanum complex 31, no such decoalescence
was observed, even at -60 ˚C.
The benzyl methylene protons are diastereotopic at ambient temperature for all these
complexes with an exception of the scandium complex 29. For example, the 1H resonances
(in benzene-d6 at 25 ˚C) were found at δ 2.22 and 1.96 ppm (JHH = 7.1 Hz and JYH = 2.7 Hz)
for 27, and δ 2.27 and 1.91 ppm (JHH = 7.4 Hz and JYH = 2.0 Hz) for 30. The corresponding 13C resonances are found at δ 51.4 ppm (JCH = 120.7 Hz and JYC = 28.2 Hz) for 27 and δ 52.4
ppm (JCH = 122.9 Hz and JYC = 28.9 Hz) for 30. For the four benzyl methylene protons of 29,
a single 1H resonance at δ 2.19 ppm was observed at ambient temperature, and those four
protons are diastereotopic at -35 ˚C, with resonances at δ 2.22 and 2.18 ppm (JHH = 8.8 Hz).
For 26-28, the coupling constant 1JCH increases from 114.8 Hz via 120.7 Hz to 134.0 Hz,
indicative of the above-mentioned differences in coordination mode of the benzyl groups as
function of the metal center. This trend was also observed for complexes 29-31, with
coupling constants 1JCH of 114.2, 122.9 and 135.7 Hz respectively.
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
93
5.2.2 Synthesis of Me4DAPA-Amide Metal Dibenzyl Complexes (L12)M(CH2Ph)2
(M = Sc, Y, and La)
Reaction of the rare earth metal tribenzyls M(CH2Ph)3(THF)3 with the Me4DAPA-Amide
ligand precursor HL12 in THF solvent afforded the dibenzyl complexes (L12)M(CH2Ph)2 (M
= Sc, 33; M = Y, 34; M = La, 35) as crystalline materials after crystallization from a
THF/n-hexane mixture (isolated yield: 33, 72%; 34, 79%; 35, 75%) (Scheme 5.2). When
performed in THF-d8, these reactions were seen by NMR spectroscopy to be quantitative.
These complexes are highly air and moisture sensitive, but thermally robust and can be
stored in the solid state or solution at ambient temperature for a few months without
decomposition.
Scheme 5.2. Synthesis of Dibenzyl Complexes 33-35.
The 1H NMR spectra of these complexes in THF-d8 reveal fully asymmetric structures,
as seen e.g. by two methyl resonances for the SiMe-group (δ 0.40 and 0.30 ppm for 33; δ
0.35 and 0.21 ppm for 34; δ 0.30 and 0.22 ppm for 35). For each complex, two sets of 1H
NMR resonances for the M-CH2 groups were observed: the benzyl methylene protons are
diastereotopic. Their 1H NMR resonances (in THF-d8) are at δ 2.18 and 2.09 ppm (d, JHH =
8.4 Hz) and δ 2.04 and 1.94 ppm (d, JHH = 8.8 Hz) for 33, δ 1.81 and 1.79 ppm and δ 1.77
and 1.64 ppm (dd, JHH = 8.1 Hz, JYH = 3.3 Hz) for 34, and δ 1.80 and 1.77 ppm and δ 1.77
and 1.17 ppm (br., JHH not resolved) for 35. The corresponding 13C resonances are found at
δ 58.4 (broad triplet, JCH = 107.6 Hz) for 33, δ 56.0 ppm (dt, JCH = 116.0 Hz, JYC = 30.6 Hz)
and 55.1 (dt, JCH = 117.3 Hz, JYC = 33.4 Hz) for 34, and δ 67.0 and 66.2 ppm (t, JCH = 121.9
Hz) for 35.
Chapter 5
94
Figure 5.2. Molecular structures of complex 33-35. All hydrogen atoms are omitted for
clarity and thermal ellipsoids are drawn at the 50% probability level.
Table 5.2. The Geometric Data of Complexes 33-35.
33 (M = Sc) 35 (M = La) 34
M-N(1) 2.466(2) 2.7576(17) Y(1)-N(11) 2.607(2)
M-N(2) 2.399(2) 2.7838(18) Y(1)-N(12) 2.545(2)
M-N(3) 2.373(2) 2.7301(17) Y(1)-N(13) 2.522(2)
M-N(4) 2.097(2) 2.3919(18) Y(1)-N(14) 2.235(2)
M-C(16) 2.325(3) 2.680(2) Y(1)-C(116) 2.487(3)
M-C(17) 3.149(2) Y(1)-C(117)
M-C(23) 2.315(3) 2.700(2) Y(1)-C(123) 2.502(3)
M-C(24) 3.041(2) Y(1)-C(124)
M-C(16)-C(17) 127.18(17) 94.91(14) Y(1)-C(116)-C(117) 109.25(17)
M-C(23)-C(24) 119.03(17) 89.17(13) Y(1)-C(123)-C(124) 116.69(18)
ΣN(4) 359.2(2) 359.72(17) ΣN(14) 359.23(15)
The structures of complexes 33-35 were established by single-crystal X-ray diffraction and
are shown in Figure 5.2, with the geometric data compiled in Table 5.2. All three complexes
contain a tetradentate ligand with the three nitrogen atoms of the 1,4-diazepan-6-amine
moiety in facial arrangement. Each metal center displays three long M-N(amino) bonds and
one shorter M-N(amido) bond, consistent with triamino-amido ligand character. The
geometry around the amido nitrogen is essentially planar, as seen by the sum of angles
around the amido nitrogen ΣN(amido) (359.2(2)º for 33, 359.72(17)º for 34, and
359.23(15)º for 35). Complexes 33 and 34 contain two η1-bound benzyl groups, with
Sc-CH2-Cipso angles of 127.18(17)º and 119.03(17)º for 33 and Y-CH2-Cipso angles of
109.25(17)º and 116.69(18)º for 34. In the lanthanum complex 35, both benzyl groups are
η2-bound with La-CH2-Cipso angles of 94.91(14)º and 89.17(13)º. This data indicate that
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
95
the Me4DAPA-amido ligand L12 is sterically more demanding than the Me3DAPA-amino
ligands L6 and L8.
5.2.3 Synthesis of Me3DAPA-Amidine Metal Dialkyl Complexes (L)M(CH2SiMe3)2
(L = L9 and L10, M = Sc and Y)
Reaction of the group 3 metal trialkyls M(CH2SiMe3)3(THF)2 (M = Sc and Y)5 with the
ligand precursors HL9 or HL10 in toluene afforded the dialkyl complexes (L)M(CH2SiMe3)2
(L = L9, M = Sc, 36; L = L9, M = Y, 37; L = L10, M = Sc, 38; L = L10, M = Y, 39) via the
well-established TMS elimination route,6 as shown in Scheme 5.3. They were obtained as
off-white microcrystalline solids in 70-80% isolated yield after crystallization from
toluene/n-hexane mixtures. For the scandium complexes 36, their 1H NMR spectra show a
single resonance for the four ScCH2 methylene protons and it is found at δ 0.13 ppm, with the
corresponding 13C resonances present at δ 35.9 ppm. For the yttrium complexes 37 and 39,
the YCH2 methylene protons are diastereotopic; their 1H NMR resonances are found at δ
-0.19 and -0.31 ppm (dd, JHH = 11.1 Hz, JYH = 2.8 Hz) for 37 and δ -0.25 and -0.45 ppm (dd,
JHH = 11.0 Hz, JYH = 2.6 Hz) for 39 and the corresponding 13C NMR resonances are at δ 32.4
ppm (dt, JCH = 101.3 Hz and JYC = 37.8 Hz) and δ 33.6 ppm (dt, JCH = 100.2 Hz and JYC =
37.6 Hz), respectively. Attempts to generate the lanthanum dibenzyl or alkyl complexes did
not result in well-defined species.
Scheme 5.3. Synthesis of Dialkyl Complexes 36-39.
The structures of 36-39 were determined by single-crystal X-ray diffraction and are
shown in Figure 5.3, with the geometric data listed in Table 5.3. All these complexes show
an approximately octahedral geometry, with the three nitrogen atoms of the
1,4-diazepan-6-amine moiety in facial arrangement. The amidinate moiety N(1)-C(7)-N(2)
seems to be conjugated, as seen by the very small difference between the N(1)-C(7) and
N(2)-C(7) bond distances (max. 0.010 Å in 36). Nevertheless, whereas the geometry around
N(1) of the amidinate moiety in all complexes 36-39 is planar, the other nitrogen N(2)
Chapter 5
96
deviates significantly from planarity as seen by the sum of the angles around N(2) (ranges
from 330.55º to 334.13º, see table 5.3), which might be due to the constraint imposed by
the coordination of 1,4-diazpen-6-amine moiety to the metal center. The M-N(1) and
M-N(2) distances in each of the complexes do not differ greatly, with the maximum
difference of 0.09 Å for complex 37, but with M-N(2) being consistently the shorter of the
two distances. The two amino nitrogen atoms of the 1,4-diazepan-6-amine moiety are
bound to the metal center in an asymmetric fashion with the difference of min. 0.10 Å for
37 and max. 0.31 Å for 39 between these two M-N bond distances. In comparing the
scandium complexes 36 and 38, it can be seen that the more sterically demanding
substituent on L10 in 38 pushes the alkyl SiMe3 substituents away from the metal, as seen
from the Sc-C-Si angles: 127.4(2)º and 124.09(19)º in 36, versus 143.91(17)º and
138.36(17)º in 38. For the larger metal yttrium, this difference is much smaller.
Figure 5.3. Molecular structures of complexes 36-39. All hydrogen atoms are omitted
for clarity and thermal ellipsoids are drawn at the 50% probability level.
36 37
38 39
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
97
Table 5.3. The Geometric Data of Complexes 36-39.
36 (M = Sc) 38 (M = Sc) 37 (M = Y) 39 (M = Y)
M(1)-N(1) 2.222(3) 2.274(2) 2.3664(14) 2.359(2)
M(1)-N(2) 2.181(3) 2.183(2) 2.3305(14) 2.353(2)
M(1)-N(3) 2.569(3) 2.569(2) 2.5562(15) 2.812(2)
M(1)-N(4) 2.391(3) 2.389(2) 2.6556(15) 2.504(2)
M(1)-C(22) 2.282(4) 2.260(3) 2.4217(19) 2.462(3)
M(1)-C(26) 2.252(4) 2.243(3) 2.4519(18) 2.420(3)
C(7)-N(1) 1.333(4) 1.339(3) 1.347(2) 1.342(3)
C(7)-N(2) 1.343(4) 1.335(3) 1.337(2) 1.334(3)
N(1)-M(1)-N(2) 60.41(10) 60.13(8) 56.89(5) 56.65(7)
M(1)-C(22)-Si(1) 127.4(2) 143.91(17) 121.86(9) 122.90(14)
M(1)-C(26)-Si(2) 124.09(19) 138.36(17) 122.50(9) 127.14(13)
ΣN(1) 360.0(3) 359.83(2) 359.96(14) 359.53(2)
ΣN(2) 330.55(3) 333.80(2) 334.13(13) 333.80(2)
ΣC(7) 360.1(3) 359.9(2) 359.99(14) 360.1(2)
5.3 Generation of Cationic Species [(L)M(CH2R)]+ (R = Ph or SiMe3)
Upon reaction with 1 equiv of [PhNMe2H][B(C6F5)4] in the weakly coordinating polar
solvent C6D5Br, the dibenzyl complexes 26-31 and 33-35 are cleanly converted to the
corresponding cationic monobenzyl species [(L)M(CH2Ph)]+ (as seen by NMR
spectroscopy) with liberation of toluene and free PhNMe2. The cationic monobenzyl
scandium and yttrium species are sufficiently stable to allow characterization by both 1H
and 13C NMR spectroscopy at ambient temperature. The cationic monobenzyl lanthanum
species in C6D5Br decompose within an hour at ambient temperature and precipitate as a
brown oily material; after decomposition, only toluene and PhNMe2 could be detected in
solution by 1H NMR spectroscopy. The cationic species show the typical downfield shift for
the M-CH2Ph 13C resonances relative to their neutral dibenzyl precursors;6 for example, the
cationic species [(L6)YCH2Ph]+ shows a 13C NMR resonance at δ 53.7 ppm for the YCH2
group, while the 13C NMR resonance for the YCH2 group in the neutral complex
(L6)Y(CH2Ph)2 is present at δ 51.4 ppm.
In contrast to the above-mentioned dibenzyl complexes, no well-defined species were
observed for reactions of dialkyl complexes 32 and 36-39 upon reaction with
[PhNMe2H][B(C6F5)4] in C6D5Br. Apparently, the initially formed cationic species are
thermal labile and decompose through ligand H-abstraction processes, since liberation of
Chapter 5
98
two equiv of TMS were observed for each reaction. For the cationic yttrium monoalkyl
species [(L6)Y(CH2SiMe3)]+, such decomposition can be prevented when the reaction is
carried out in THF solvent. This species shows a typical downfield-shifted 13C NMR
resonance with an increase in the 1JYC coupling constant for YCH2 (13C NMR in THF-d8: δ
28.9 ppm, 1JYC = 38.8 Hz vs 32: δ 27.9 ppm, 1JYC = 36.2 Hz). For cationic species
generated from dialkyl complexes 36-39, rapid decomposition still takes place even in THF.
5.4 Concluding Remarks
We have shown that monoanionic tetradentate ligands L6, L8, and L12 are suitable to
support neutral dibenzyl and cationic monobenzyl complexes of scandium, yttrium, and
lanthanum and thus can be used over the full size range of the rare earth metals. However,
only scandium and yttrium dialkyl complexes could be prepared for the Me3DAPA
-amidinate ligands L9 and L10. The synthesis of these complexes offers us a basis to study
the effects of the metal ion size, the ancillary ligand, and the use of neutral vs cationic catalyst
on catalyst performances for reactions catalyzed by these complexes. In Chapter 6, the effects
of these factors on the catalytic dimerization of terminal alkynes are described.
5.5 Experimental Section
General Remarks. See the corresponding section in Chapter 2. M(CH2SiMe3)3(THF)2 (M
= Sc and Y)5, Sc(CH2Ph)3(THF)3,2a La(CH2Ph)3(THF)3
2c were prepared according to
published procedures. Y(CH2Ph)3(THF)3 is readily accessible via the same procedure as used for
the other tribenzyl complexes.
General procedure for synthesis of 26-31. A solution of HL6 or HL8 (1 mmol) in toluene
or THF (5 mL) was added to a solution of M(CH2Ph)3(THF)3 (1 mmol) in toluene or THF (20
mL) and the resulting mixture was stirred at room temperature for 30 min. All the volatiles
were removed under reduced pressure and the residue was dissolved in toluene (~ 3 mL).
Pentane or n-hexane (5 mL) was carefully layered on top of the resulting red solution. Upon
cooling to -30 °C, crystalline material formed. The mother liquor was decanted and the solid
was dried under reduced pressure, affording the corresponding dibenzyl compound as a
crystalline solid.
Synthesis of (L6)Sc(CH2Ph)2 (26). Starting materials: Sc(CH2Ph)3(THF)3 (0.24 g, 0.52
mmol) and HL6 (0.13 g, 0.52 mmol); Yield: 0.19 g, (0.40 mmol, 77%). 1H NMR (500MHz,
C6D6) δ: 7.28-7.20 (8H, o-H + m-H, Ph), 6.81 (t, 2H, JHH = 6.6 Hz, p-H Ph), 2.75 (m, 2H, Py
α-H), 2.71 (m, 2H, NCH2-bridge), 2.65 (m, 2H, NCH2-bridge), 2.48 (m, 2H, NCH2), 2.45 (d,
2H, JHH = 12.0 Hz, CCH2), 2.24 (d, 2H, JHH = 8.4 Hz, ScCH2), 2.22 (m, 2H, Py α-H), 2.11 (d,
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
99
2H, JHH = 8.4 Hz, ScCH2), 2.07 (s, 6H, NCH3), 1.70 (d, 2H, JHH = 12.0 Hz, CCH2), 1.60 (m,
2H, NCH2), 1.35 (m, 2H, Py β-H), 1.29 (m, 2H, Py β-H), 0.59 (s, 3H, CCH3). 13C NMR
(125.7 MHz, C6D6) δ: 155.5 (s, ipso-C Ph), 128.5 (d, JCH = 151.0 Hz, o-C Ph), 124.4 (d, JCH =
152.6 Hz, m-C Ph), 117.2 (d, JCH = 159.3 Hz, p-C Ph), 74.0 (t, JCH = 134.3 Hz, CCH2), 57.6 (t,
JCH = 132.2 Hz, NCH2), 57.3 (s, CCH3), 57.0 (t, JCH = 135.2 Hz, NCH2-bridge), 52.5 (t, JCH =
138.4 Hz, α-C Py), 52.3 (t, JCH =114.8 Hz, ScCH2), 50.6 (q, JCH = 136.2 Hz, NCH3), 45.5 (t,
JCH = 129.4 Hz, NCH2-bridge), 22.4 (t, JCH = 132.0 Hz, β-C Py), 20.3 (q, JCH = 125.9 Hz,
CCH3). Anal. Calc for C28H43N4Sc: C, 69.97; H, 9.02; N, 11.66. Found: C: 69.50; H, 9.03; N,
11.26.
Synthesis of (L6)Y(CH2Ph)2 (27). Starting materials: Y(CH2Ph)3(THF)3 (0.63 g, 1.10
mmol) and HL6 (0.28 g, 1.10 mmol); Yield: 0.45 g, (0.86 mmol, 80%). 1H NMR (400MHz,
C6D6) δ: 7.19-7.11 (8H, o-H + m-H, Ph), 6.65 (t, 2H, JHH = 6.4 Hz, p-H Ph), 2.89 (m, 2H, α-H
Py), 2.82 (m, 2H, NCH2-bridge), 2.77 (m, 2H, NCH2-bridge), 2.51 (d, 2H, JHH = 11.7 Hz,
CCH2), 2.29 (m, 2H, α-H Py), 2.22 (dd, 2H, JHH = 7.12 Hz, JYH = 2.7 Hz,YCH2), 2.01 (s, 6H,
NCH3), 1.96 (dd, 2H, JHH = 7.12 Hz, JYH = 2.7 Hz,YCH2), 1.87 (m, 2H, NCH2), 1.71 (d, 2H,
JHH = 11.7 Hz, CCH2), 1.48 (m, 2H, NCH2), 1.43 (m, 2H, β-H Py), 1.38 (m, 2H, β-H Py), 0.66
(s, 3H, CCH3). 13C NMR (100.5 MHz, C6D6) δ: 155.0 (s, ipso-C Ph), 129.8 (d, JCH = 153.6 Hz,
o-C Ph), 122.3 (d, JCH = 154.4 Hz, m-C Ph), 116.1 (d, JCH = 159.0 Hz, p-C Ph), 74.9 (t, JCH =
133.4 Hz, CCH2), 59.1 (t, JCH = 136.1 Hz, NCH2-bridge), 57.3 (t, JCH = 137.9 Hz, NCH2),
57.0 (s, CCH3), 52.6 (t, JCH = 138.7 Hz, α-C Py), 51.4 (dt, JCH =120.7 Hz, JYC = 28.2 Hz,
YCH2), 49.6 (q, JCH = 127.6 Hz, NCH3), 46.3 (t, JCH = 126.6 Hz, NCH2-bridge), 23.0 (t, JCH =
132.4 Hz, β-C Py), 20.6 (q, JCH = 124.0 Hz, CCH3). Anal. Calc for C28H43N4Y: C, 64.11; H,
8.26; N, 10.68. Found: C: 64.21; H, 8.32; N, 10.35.
Synthesis of (L6)La(CH2Ph)2 (28). Starting materials: La(CH2Ph)3(THF)3 (0.898 g, 1.57
mmol) and HL6 (0.364 g, 1.57 mmol); Yield: 0.615 g, (1.07 mmol, 68%). 1H NMR (400MHz,
C6D6) δ: 7.07 (t, 4H, JHH = 7.57 Hz, m-H Ph), 6.70 (d, 4H, JHH = 7.76 Hz, o-H Ph), 6.47 (t, 2H,
JHH = 7.17 Hz, p-H Ph), 2.88 (m, 2H, NCH2-bridge), 2.80 (m, 2H, NCH2-bridge), 2.67 (m, 2H,
α-H Py), 2.62 (d, 2H, JHH = 12.1 Hz, CCH2), 2.34 (br, 2H, LaCH2), 2.14 (m, 2H, α-H Py),
2.11 (br, 2H, LaCH2), 2.10 (m, 2H, NCH2), 2.02 (s, 6H, NCH3), 1.83 (d, 2H, JHH = 12.1 Hz,
CCH2), 1.63 (m, 2H, NCH2), 1.55 (m, 2H, Py β-H), 1.42 (m, 2H, Py β-H), 0.67 (s, 3H, CCH3). 13C NMR (100.5 MHz, C6D6) δ: 152.2 (s, ipso-C Ph), 131.0 (d, JCH = 153.5 Hz, m-C Ph),
120.7 (d, JCH = 152.0 Hz, o-C Ph), 114.3 (d, JCH = 159.4 Hz, p-C Ph), 73.7 (t, JCH = 134.3 Hz,
CCH2), 62.6 (t, JCH =134.0 Hz, LaCH2), 59.4 (s, CCH3), 58.5 (t, JCH = 133.6 Hz,
NCH2-bridge), 57.3 (t, JCH = 131.9 Hz, NCH2), 52.9 (t, JCH = 138.5 Hz, α-C Py), 49.4 (q, JCH
= 135.2 Hz, NCH3), 47.6 (t, JCH = 128.7 Hz, NCH2-bridge), 23.3 (t, JCH = 131.3 Hz, β-C Py),
20.9 (q, JCH = 125.0 Hz, CCH3). Anal. Calc for C28H43LaN4: C, 58.53; H, 7.54; N, 9.75.
Found: C: 58.75; H, 7.60; N, 9.34.
Chapter 5
100
Synthesis of (L8)Sc(CH2Ph)2 (29). Starting materials: Sc(CH2Ph)3(THF)3 (0.481 g, 0.90
mmol) and HL8 (0.256 g, 0.9 mmol). Yield: 0.349 g, (0.68 mmol, 76%). 1H NMR (500MHz,
C6D6) δ: 7.23 (m, 8H, o, m-H Ph), 6.83 (m, 2H, p-H Ph), 2.87 (m, 4H, α-H Py), 2.44 (m, 2H,
NCH2), 2.19 (s, 4H, ScCH2), 2.15 (d, 2H, JHH = 11.5 Hz, CCH2), 2.05 (s, 6H, NCH3), 1.72 (d,
2H, JHH = 11.5 Hz, CCH2), 1.56 (m, 2H, NCH2), 1.46 (m, 4H, β-H Py), 0.61 (s, 3H, CCH3),
0.11 (s, 6H, Si(CH3)2). 13C (75.4 MHz, C6D6) δ: 154.8 (s, ipso-C Ph), 128.5 (d, JCH = 153.8
Hz, o-C Ph), 124.6 (d, JCH = 154.2 Hz, m-C Ph), 117.8 (d, JCH = 158.3 Hz, p-C Ph), 78.3 (t,
JCH = 135.6 Hz, CCH2), 57.4 (t, JCH = 133.8 Hz, NCH2), 56.5 (s, CCH3), 54.1 (t, JCH = 114.2
Hz, ScCH2), 50.7 (q, JCH = 132.2 Hz, NCH3), 49.8 (t, JCH = 138.7 Hz, α-C Py), 25.6 (t, JCH =
130.8 Hz, β-C Py), 25.3 (q, JCH = 125.4 Hz, CCH3), 2.46 (q, JCH = 117.5 Hz, Si(CH3)2). Anal.
Calc for C28H45N4ScSi: C, 65.68; H, 8.88; N, 10.97. Found: C: 65.37; H, 8.87; N, 10.85.
Synthesis of (L8)Y(CH2Ph)2 (30). Starting materials: Y(CH2Ph)3(THF)3 (0.365 g, 0.63
mmol) and HL8 (0.179 g, 0.63 mmol). Yield: 0.247 g, (0.45 mmol, 71%). 1H NMR (500MHz,
C6D6) δ: 7.14 (t, 4H, JHH = 7.6 Hz, m-H Ph), 7.05 (d, 4H, JHH = 7.5 Hz, o-H Ph), 6.62 (t, 2H,
JHH = 7.2 Hz, p-H Ph), 2.96 (m, 4H, α-H Py), 2.27 (dd, 2H, JHH = 7.4 Hz, JYH = 2.0 Hz, YCH2),
2.16 (d, 2H, JHH = 11.6 Hz, CCH2), 2.00 (s, 6H, NCH3), 1.91 (dd, 2H, JHH = 7.4 Hz, JYH = 2.0
Hz, YCH2), 1.78 (m, 2H, NCH2), 1.72 (d, 2H, JHH = 11.6 Hz, CCH2), 1.55 (m, 4H, β-H Py),
1.42 (m, 2H, NCH2), 0.66 (s, 3H, CCH3), 0.19 (s, 6H, Si(CH3)2). 13C NMR (126.5 MHz, C6D6)
δ: 154.7 (s, ipso-C Ph), 130.1 (d, JCH = 154.4 Hz, m-C Ph), 121.8 (d, JCH = 152.6 Hz, o-C Ph),
116.3 (d, JCH = 159.6 Hz, p-C Ph), 79.0 (t, JCH = 134.8 Hz, CCH2), 56.9 (t, JCH = 144.3 Hz,
NCH2), 55.8 (s, CCH3), 52.4 (dt, JCH = 122.9 Hz, JYC = 28.9 Hz, YCH2), 49.7 (t, JCH = 138.5
Hz, α-C Py), 49.6 q, JCH = 134.8 Hz, NCH3), 25.8 (t, JCH = 132.1 Hz, β-C Py), 25.7 (q, JCH =
125.1 Hz, CCH3), 3.23 (q, JCH = 117.0 Hz, Si(CH3)2). Anal. Calc for C28H45N4SiY: C, 60.63;
H, 8.18; N, 10.10. Found: C: 60.04; H, 8.66; N, 9.65.
Synthesis of (L8)La(CH2Ph)2 (31). Starting materials: La(CH2Ph)3(THF)3 (0.447 g, 0.71
mmol) and HL8 (0.202 g, 0.71 mmol). Yield: 0.336 g, (0.56 mmol, 79%). 1H NMR (500MHz,
C6D6) δ: 7.08 (t, 4H, JHH = 7.4 Hz, m-H Ph), 6.52 (d, 4H, JHH = 7.3 Hz, o-H Ph), 6.50 (t, 2H,
JHH = 7.3 Hz, p-H Ph), 2.70 (m, 4H, α-H Py), 2.25 (d, 2H, JHH = 11.4 Hz, CCH2), 2.23 (br, 2H,
LaCH2), 2.21 (m, 2H, NCH2), 2.07 (br, 2H, LaCH2), 2.04 (s, 6H, NCH3), 1.88 (d, 2H, JHH =
11.4 Hz, CCH2), 1.63 (m, 2H, NCH2), 1.55 (m, 4H, β-H Py), 0.69 (s, 3H, CCH3), 0.14 (s, 6H,
Si(CH3)2). 13C (75.4 MHz, C6D6) δ: 152.2 (s, ipso-C Ph), 131.2 (d, JCH = 154.1 Hz, o-C Ph),
120.2 (d, JCH = 150.2 Hz, m-C Ph), 114.5 (d, JCH = 159.3 Hz, p-C Ph), 78.1 (t, JCH = 133.0 Hz,
CCH2), 54.1 (t, JCH = 135.7 Hz, LaCH2), 57.7 (s, CCH3), 57.1 (t, JCH = 135.7 Hz, NCH2), 49.6
(q, JCH = 135.8 Hz, NCH3), 48.5 (t, JCH = 136.5 Hz, α-C Py), 26.5 (t, JCH = 130.0 Hz, β-C Py),
26.1 (q, JCH = 125.5 Hz, CCH3), 3.24 (q, JCH = 117.1 Hz, Si(CH3)2). Anal. Calc for
C28H45LaN4Si: C, 55.62; H, 7.50; N, 9.27. Found: C: 55.56; H, 7.53; N, 9.11.
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
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Synthesis of (L6)Y(CH2SiMe3)2 (32). A solution of ligand HL6 (0.29 g, 1.15 mmol) in
toluene (20 ml) was added dropwise to a solution of Y(CH2SiMe3)3(THF)2 (0.57 g, 1.15
mmol) at 0 °C. The mixture was stirred at room temperature for 30 min and then all the
volatiles were removed under vacuum. The residue was dissolved in 4 ml of n-hexane,
filtered, and the filtrate was stored at -30 ˚C overnight. The title compound (0.43 g, 0.83
mmol, 72%) was isolated as slightly yellow crystals. 1H NMR (500 MHz, C7D8) δ: 3.07 (m,
2H, NCH2), 2.79 (m, 2H, NCH2), 2.75 (s, 4H, NCH2), 2.50 (d, 2H, JHH = 12.0 Hz, CCH2),
2.24 (m, 2H, NCH2), 2.20 (s, 6H, NCH3), 1.81 (d, 2H, JHH = 12.0 Hz, CCH2), 1.75 (m, 2H,
NCH2), 1.63 (broad, 2H, NCH2), 1.39 (broad, 2H, NCH2), 0.72 (s, 3H, CCH3), 0.41 (s, 18H,
Si(CH3)3), -0.74 (dd, 2H, JHH = 10.9 Hz, JYH = 2.7 Hz, YCH2), -0.95 (dd, 2H, JHH = 10.9 Hz,
JYH = 2.7 Hz, YCH2). 13C NMR (125.7 MHz, 298K, C7D8, δ): 73.5 (t, JCH = 132.8 Hz, CCH2),
60.1 (t, JCH = 139.2 Hz, NCH2-bridge), 57.6 (s, CCH3), 57.3 (t, JCH = 136.7 Hz, NCH2), 52.8
(t, JCH = 136.7 Hz, α-C Py), 50.1 (q, JCH = 131.6 Hz, NCH3), 46.0 (t, JCH = 126.6 Hz,
NCH2-bridge), 27.2 (dt, JCH = 100.6 Hz, JYC = 36.7 Hz, YCH2), 23.0 (t, JCH = 132.4 Hz, β-C
Py), 20.8 (q, JCH = 125.7 Hz, CCH3), 5.3 (q, JCH = 117.2 Hz, Si(CH3)3). Anal. Calc for
C22H51N4Si2Y: C, 51.13; H, 9.95; N, 10.84. Found: C, 51.00; H, 9.90; N, 10.75.
Synthesis of (L12)Sc(CH2Ph)2 (33). A solution HL12 (180.3 mg, 0.6 mmol) in THF (2
mL) was added to a solution of Sc(CH2Ph)3(THF)3 (320.8 mg, 0.6 mmol) in THF (20 mL)
and the resulting solution was stirred at room temperature for 20 min. Then all the volatiles
were removed under reduced pressure and the residue was purified by crystallization from a
THF/n-hexane mixture, yielding the title compound (226.5 mg, 0.43 mmol, 72%) as an
off-white crystalline solid. 1H NMR (500 MHz, THF-d8) δ: 6.88 (d, 2H, JHH = 7.5 Hz, o-H
Ph), 6.81 (d, 2H, JHH = 7.5 Hz, o-H Ph), 6.85 (t, 4H, JHH = 6.8 Hz, m-H Ph), 6.42 (t, 1H, JHH
= 6.9 Hz, p-H Ph), 6.39 (t, 1H, JHH = 6.9 Hz, p-H Ph), 3.51 (d, 1H, JHH = 14.0 Hz, CCH2),
3.26 (d, 1H, JHH = 14.7 Hz, CCH2), 2.88 (m, 1H, NCH2), 2.84 (m, 1H, NCH2), 2.62 (s, 3H,
NCH3), 2.54 (s, 3H, NCH3), 2.42 (m, 1H, NCH2), 2.39 (d, 1H, JHH = 14.7 Hz, CCH2), 2.32
(d, 1H, JHH = 14.0 Hz, CCH2), 2.29 (s, 3H, NCH3), 2.22 (m, 1H, NCH2), 2.18 (d, 1H, JHH =
8.4 Hz, ScCH2), 2.09 (d, 1H, JHH = 8.4 Hz, ScCH2), 2.04 (d, 1H, JHH = 8.8 Hz, ScCH2),
1.94 (d, 1H, JHH = 8.8 Hz, ScCH2), 1.38 (s, 9H, C(CH3)3), 0.94 (s, 3H, CCH3), 0.40 (s, 3H,
SiCH3), 0.30 (s, 3H, SiCH3). 13C (THF-d8,100.6 Hz) δ: 157.8 (s, ipso-C Ph), 157.3 (s,
ipso-C Ph), 129.5 (d, JCH = 154.4 Hz, m-C Ph), 129.3 (d, JCH = 153.0 Hz, m-C Ph), 126.0 (d,
JCH = 153.3 Hz, o-C Ph), 125.1 (d, JCH = 153.3 Hz, o-C Ph), 118.5 (d, JCH = 153.3 Hz, p-C
Ph), 118.1 (d, JCH = 158.7 Hz, p-C Ph), 75.6 (t, JCH = 136.0 Hz, CCH2), 68.8 (t, JCH = 135.9
Hz, CCH2), 61.3 (s, C(CH3)3), 60.4 (t, JCH = 137.8 Hz, NCH2), 59.7 (t, JCH = 137.8 Hz,
NCH2), 54.9 (s, CCH3), 58.4 (t, JCH = 107.6 Hz, ScCH2), 51.9 (q, JCH = 136.4 Hz, NCH3),
51.5 (q, JCH = 136.4 Hz, NCH3), 38.0 (q, JCH = 126.5 Hz, C(CH3)3), 35.4 (t, JCH = 137.8 Hz,
NCH3), 19.1 (t, JCH = 127.4 Hz, CCH3), 10.5 (q, JCH = 118.5 Hz, SiCH3), 9.8 (q, JCH =
Chapter 5
102
118.5 Hz, SiCH3). Anal. Calc for C29H49N4ScSi: C, 66.12; H, 9.38; N, 10.64. Found: C: 65.89;
H, 9.40; N, 10.39.
Synthesis of (L12)Y(CH2Ph)2 (34). This complex was synthesized according to the
procedure described for 33, with HL12 (180.3 mg, 0.6 mmol) and Y(CH2Ph)3(THF)3 (347.2
mg, 0.6 mmol) as starting materials. Purification by crystallization from a THF/n-hexane
solution yielded the title compound (280.3 mg, 0.47 mmol, 79%) as an off-white crystalline
solid. 1H NMR (400 MHz, THF-d8) δ: 6.81 (t, 4H, JHH = 7.3 Hz, m-H Ph), 6.77 (d, 2H, JHH
= 8.1 Hz, o-H Ph), 6.69 (d, 2H, JHH = 8.1 Hz, o-H Ph), 6.31 (t, 2H, JHH = 7.3 Hz, p-H Ph),
3.52 (dd, 1H, JHH = 14.3 Hz, CCH2), 3.10 (dd, 1H, JHH = 14.9 Hz, CCH2), 2.88 (m, 1H,
NCH2), 2.82 (m, 1H, NCH2), 2.59 (m, 1H, NCH2), 2.58 (s, 3H, NCH3), 2.45 (s, 3H, NCH3),
2.41 2.82 (m, 1H, NCH2), 2.36 (d, 1H, JHH = 14.9 Hz, CCH2), 2.28 (s, 3H, NCH3), 2.27 (d,
1H, JHH = 14.3 Hz, CCH2), 2.16 (m, 1H, NCH2), 1.81 (dd, 1H, JHH = 8.1 Hz, JYH = 3.3 Hz,
YCH2), 1.79 (dd, 1H, JHH = 8.1 Hz, JYH = 3.3 Hz, YCH2), 1.77 (dd, 1H, JHH = 8.1 Hz, JYH =
3.3 Hz, YCH2), 1.64 (dd, 1H, JHH = 8.1 Hz, JYH = 3.3 Hz, YCH2), 1.27 (s, 9H, C(CH3)3),
0.91 (s, 3H, CCH3), 0.35 (s, 3H, SiCH3), 0.21 (s, 3H, SiCH3). 13C (THF-d8,100.6 Hz) δ:
157.4 (s, ipso-C Ph), 157.0 (s, ipso-C Ph), 129.9 (d, JCH = 154.0 Hz, m-C Ph), 129.7 (d, JCH
= 152.7 Hz, m-C Ph), 125.1 (d, JCH = 152.0 Hz, o-C Ph), 124.1 (d, JCH = 152.0 Hz, o-C Ph),
117.4 (d, JCH = 156.7 Hz, p-C Ph), 117.2 (d, JCH = 156.7 Hz, p-C Ph), 75.6 (t, JCH = 136.0
Hz, CCH2), 66.9 (t, JCH = 135.7 Hz, CCH2), 61.4 (s, C(CH3)3), 59.9 (t, JCH = 135.7 Hz,
NCH2), 58.3 (t, JCH = 135.7 Hz, NCH2), 56.0 (dt, JCH = 116.0 Hz, JYC = 30.6 Hz, YCH2),
55.1 (dt, JCH = 117.3 Hz, JYC = 33.4 Hz, YCH2), 54.0 (s, CCH3),51.9 (q, JCH = 136.4 Hz,
NCH3), 50.5 (q, JCH = 135.7 Hz, NCH3), 50.2 (q, JCH = 135.7 Hz, NCH3), 37.8 (q, JCH =
121.7 Hz, C(CH3)3), 33.9 (t, JCH = 136.9 Hz, NCH3), 19.5 (t, JCH = 125.5 Hz, CCH3), 10.6
(q, JCH = 117.9 Hz, SiCH3), 9.8 (q, JCH = 117.9 Hz, SiCH3). Anal. Calc for C29H49N4SiY: C,
61.03; H, 8.65; N, 9.82. Found: C: 59.70; H, 8.57; N, 9.55. The rather low carbon content
found (whereas H and N values agree with the calculated values) is likely due to some
carbide formation.
Synthesis of (L12)La(CH2Ph)2 (35). This complex was synthesized according to the
procedure described for 33, with HL12 (180.3 mg, 0.6 mmol) and La(CH2Ph)3(THF)3 (377.2
mg, 0.6 mmol) as starting materials. Purification by crystallization from a THF/n-hexane
mixture yielded the title compound (286.8 mg, 0.45 mmol, 75%) as a yellow crystalline
solid. 1H NMR (500 MHz, THF-d8) δ: 6.92 (t, 2H, JHH = 7.5 Hz, m-H Ph), 6.79 (t, 2H, JHH
= 7.5 Hz, m-H Ph), 6.42 (t, 2H, JHH = 7.4 Hz, o-H Ph), 6.41 (t, 2H, JHH = 7.4 Hz, o-H Ph),
6.32 (t, 1H, JHH = 7.4 Hz, p-H Ph), 6.21 (t, 1H, JHH = 7.4 Hz, p-H Ph), 3.69 (d, 1H, JHH =
13.8 Hz, CCH2), 3.11 (d, 1H, JHH = 15.0 Hz, CCH2), 2.81 (m, 1H, NCH2), 2.60 (s, 3H,
NCH3), 2.50 (s, 3H, NCH3), 2.46 (m, 1H, NCH2), 2.44 (d, 1H, JHH = 15.0 Hz, CCH2), 2.41
(s, 3H, NCH3), 2.29 (d, 1H, JHH = 13.8 Hz, CCH2), 2.27 (m, 1H, NCH2), 2.06 (m, 1H,
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
103
NCH2), 1.80 (m, 1H, LaCH2), 1.76 (m, 2H, LaCH2), 1.21 (s, 9H, C(CH3)3), 1.17 (m, 1H,
LaCH2), 0.96 (s, 3H, CCH3), 0.30 (s, 3H, SiCH3), 0.22 (s, 3H, SiCH3). 13C (THF-d8,100.6
Hz) δ: 156.2 (s, ipso-C Ph), 154.2 (s, ipso-C Ph), 132.6 (d, JCH = 153.5 Hz, m-C Ph), 130.9
(d, JCH = 153.5 Hz, m-C Ph), 122.6 (d, JCH = 151.8 Hz, o-C Ph), 116.4 (d, JCH = 159.1 Hz,
p-C Ph), 116.0 (d, JCH = 159.1 Hz, p-C Ph), 76.0 (t, JCH = 134.8 Hz, CCH2), 67.0 (t, JCH =
121.9 Hz, LaCH2), 66.2 (t, JCH = 121.9 Hz, LaCH2), 65.8 (t, JCH = 132.8 Hz, CCH2), 62.1 (s,
C(CH3)3), 59.8 (t, JCH = 132.8 Hz, NCH2), 57.3 (t, JCH = 132.8 Hz, NCH2), 54.8 (s, CCH3),
50.0 (q, JCH = 138.2 Hz, NCH3), 36.5 (q, JCH = 122.9 Hz, C(CH3)3), 34.3 (t, JCH = 134.8 Hz,
NCH3), 20.2 (t, JCH = 126.7 Hz, CCH3), 10.8 (q, JCH = 117.3 Hz, SiCH3), 9.9 (q, JCH =
117.3 Hz, SiCH3). Anal. Calc for C29H49LaN4Si.(C7H8)0.5: C, 58.54; H, 8.01; N, 8.40. Found:
C: 56.99; H, 7.91; N, 8.20. The rather low carbon content found (whereas H and N values
agree with the calculated values) is likely due to some carbide formation.
General procedure for preparation of dialkyl complexes 36-39. To a solution of
M(CH2SiMe3)3(THF)2 (M = Sc or Y, 1.0 mmol) in toluene (5 mL), was added a solution of
the ligand precursor HL9 or HL10 (1.0 mmol) in toluene (5 mL) and the resulting mixture was
stirred for 20 min at room temperature. All the volatiles were removed under reduced
pressure and the residue was purified by recrystallization at -30 ºC from toluene/n-hexane
mixtures.
Synthesis of (L9)Sc(CH2SiMe3)2 (36). Starting materials: Sc(CH2SiMe3)3(THF)2 (0.50 g,
1.11 mmol) and HL9 (0.37 g, 1.11 mmol). Yield: 0.47 g, (0.85 mmol, 77%). 1H NMR (300
MHz, C6D6) δ: 7.11-6.81 (m, 9H, o-Ph, m-Ph, p-Ph overlap), 6.74 (t, 1H, JHH = 6.46 Hz,
p-Ph), 2.96 (m, 2H, NCH2), 2.50 (d, JHH = 11.4 Hz, CCH2), 2.33 (s, 6H, NCH3), 1.68 (m, 2H,
NCH2), 1.50 (d, 2H, JHH = 12.4 Hz, CCH2), 0.49 (s, 3H, CCH3), 0.40 (s, 18H, Si(CH3)3), 0.13
(s, 4H, ScCH2). {1H}13C NMR (75.4 MHz, C6D6) δ: 175.7 (NCN), 147.3 (ipso-Ph), 135.7
(ipso-Ph), 130.1 (Ph), 129.6 (p-Ph), 128.7 (Ph), 128.1 (Ph), 123.8 (m-Ph), 122.3 (p-Ph), 75.3
(CCH2), 58.7 (CCH3), 57.7 (NCH2), 49.9 (NCH3), 35.9 (br, ScCH2), 22.1 (CCH3), 4.6
(Si(CH3)3). Anal. Calc for C29H49N4ScSi2: C, 62.78; H, 8.90; N, 10.10. Found: C, 63.3; H,
8.91; N, 9.92.
Synthesis of (L9)Y(CH2SiMe3)2 (37). Starting materials: Y(CH2SiMe3)3(THF)2 (0.49 g,
1.0 mmol) and HL9 (0.34 g, 1.0 mmol). Yield: 0.43 g, (0.72 mmol, 72%). 1H NMR (400 MHz,
C6D6) δ: 7.08 (d, 2H, JHH = 6.82 Hz, o-Ph), 7.03-6.82 (m, 7H, o-Ph, m-Ph, p-Ph overlap),
7.02 (t, 1H, JHH = 7.02 Hz, p-Ph), 2.83 (m, 2H, NCH2), 2.40 (d, 2H, JHH = 12.4 Hz, CCH2),
2.27 (s, 6H, NCH3), 1.67 (m, 2H, NCH2), 1.51 (d, 2H, JHH = 12.4 Hz, CCH2), 0.50 (s, 3H,
CCH3), 0.41 (s, 18H, Si(CH3)3), -0.19 (dd, 2H, JHH = 11.1 Hz, JYH =2.8 Hz, YCH2), -0.31 (dd,
2H, JHH = 11.1 Hz, JYH =2.8 Hz, YCH2). 13C NMR (100.5 MHz, C6D6) δ: 175.1 (s, NCN),
148.1 (s, ipso-Ph), 136.3 (s, ipso-Ph), 130.0 (d, JCH = 162.2 Hz, Ph), 129.3 (d, JCH = 160.6 Hz,
Chapter 5
104
p-Ph), 128.7 (d, JCH = 161.4 Hz, Ph), 127.9 (d, JCH = 161.5 Hz, Ph), 123.8 (d, JCH = 160.0 Hz,
m-Ph), 121.9 (d, JCH = 159.1 Hz, p-Ph), 74.6 (t, JCH = 134.4 Hz, CCH2), 58.6 (s, CCH3), 57.0
(t, JCH = 137.8 Hz, NCH2), 49.7 (q, JCH = 136.7 Hz, NCH3), 32.4 (dt, JCH = 101.3 Hz, JYC =
37.8 Hz, YCH2), 22.6 (q, JCH = 126.6 Hz, CCH3), 4.9 (q, JCH = 116.9 Hz, Si(CH3)3). Anal.
Calc for C29H49N4Si2Y: C, 58.17; H, 8.25; N, 9.36. Found: C, 58.45; H, 8.25; N, 9.26.
Synthesis of (L10)Y(CH2SiMe3)2 (39). Starting materials: Y(CH2SiMe3)3(THF)2 (0.324 g,
0.66 mmol) and HL10 (0.276 g, 0.66 mmol). Yield: 0.362 g, (0.53 mmol, 81%). 1H NMR (500
MHz, C6D6, 23 ˚C) δ: 7.16 (d, 2H, JHH = 7.7 Hz, o-H Ph), 6.92-6.75 (m, 6H, m-H, p-H Ph),
3.52 (septet, 2H, JHH = 6.7 Hz, CH(CH3)2), 3.08 (m, 2H, NCH2), 2.41 (d, 2H, JHH = 12.5 Hz,
CCH2), 2.37 (s, 6H, NCH3), 1.71 (m, 2H, NCH2), 1.54 (d, 2H, JHH = 12.5 Hz, CCH2), 1.43 (d,
6H, JHH = 6.7 Hz, CH(CH3)2), 1.17 (d, 6H, JHH = 6.7 Hz, CH(CH3)2), 0.49 (s, 3H, CCH3),
0.40 (s, 28H, Si(CH3)3), -0.25 (dd, JHH = 11.0 Hz, JYH = 2.6 Hz, YCH2), -0.45 (dd, JHH = 11.0
Hz, JYH = 2.6 Hz, YCH2). 13C NMR (125.7 MHz, C6D6, 23 ˚C) δ: 176.4 (s, NCN), 143.0 (s,
ipso-C Ph), 142.0 (s, o-C Ph), 136.3 (s, ipso-C Ph), 129.7 (d, JCH = 1158.8 Hz, Ph), 129.4 (d,
JCH = 161.3 Hz, p-Ph), 127.1 (d, JCH = 156.2 Hz, Ph), 124.4 (d, JCH = 158.8 Hz, Ph), 123.4 (d,
JCH = 155.0 Hz, Ph), 75.0 (t, JCH = 136.4 Hz, CCH2), 58.3 (s, CCH3), 57.3 (t, JCH = 138.9 Hz,
NCH2), 49.9 (q, JCH = 134.7 Hz, NCH3), 33.6 (dt, JCH = 100.2 Hz, JYC = 37.6 Hz, YCH2), 28.2
(d, JCH = 133.3 Hz, CH(CH3)2), 27.1 (q, JCH = 125.4 Hz, CH(CH3)2), 23.3 (q, JCH = 125.4 Hz,
CH(CH3)2), 23.1 (q, JCH = 125.4 Hz, CCH3), 5.0 (q, JCH = 116.9 Hz, Si(CH3)3). Anal. Calc for
C35H61N4Si2Y: C, 61.55; H, 9.00; N, 8.02. Found: C, 62.38; H, 9.24; N, 7.95.
Procedure for in-situ generation of [(L)MCH2Ph]+ cations. A solution of
(L)M(CH2Ph)2 (30 μmol) in C6D5Br (0.5 mL) was added to [PhNMe2H][B(C6F5)4] (24.3 mg,
30 μmol). The resulting mixture was homogenized by agitation and transferred to an NMR
tube equipped with a Teflon (Young) valve. NMR analysis indicated clean conversion to the
corresponding cationic monobenzyl species, toluene, and free PhNMe2.
[(L6)ScCH2Ph][B(C6F5)4]. 1H NMR (500 MHz, C6D5Br, 23 ˚C) δ: 7.05 (t, 2H, JHH = 7.1
Hz, m-H Ph), 6.65 (t, 1H, JHH = 7.2 Hz, p-H Ph), 6.04 (br, 2H, o-H Ph), 2.82 (br, 2H,
NCH2-bridge), 2.70 (m, 2H, α-H Py), 2.63 (m, 2H, α-H Py), 2.60 (d, 2H, JHH = 12.4 Hz,
CCH2), 2.56 (br, 2H, NCH2-bridge), 2.15 (d, 2H, JHH = 12.4 Hz, CCH2), 2.06 (s, 6H, NCH3),
1.96 (m, 2H, NCH2), 1.87 (m, 2H, NCH2), 1.82 (br, 2H, ScCH2), 1.68 (m, 2H, β-H Py), 1.61
(m, 2H, β-H Py), 0.44 (s, 3H, CCH3). {1H}13C NMR (125.7 MHz, C6D5Br, 25 ˚C) δ: 152.4 (s,
ipso-C Ph), 148.5 (d, JCF = 240.7 Hz, o-C C6F5), 138.3 (d, JCF = 235.0 Hz, p-C C6F5), 136.5 (d,
JCF = 242.9 Hz, m-C C6F5), 133.7 (m-C Ph), 120.7 (o-C, Ph), 120.2 (p-C Ph), 124.2 (br,
ipso-C C6F5), 77.3 (CCH2N), 56.9 (Azepane-NCH2-bridge), 55.6 (NCH2CH2), 55.5 (s,
CCH3), 54.7 (ScCH2), 54.0 (α-C Py), 48.7 (NCH3), 44.9 (Py-CH2-bridge), 21.5 (β-C Py),
18.0 (CCH3).
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
105
[(L6)YCH2Ph][B(C6F5)4]. 1H NMR (500 MHz, C6D5Br, 25 ˚C) δ: 6.89 (br, 2H, m-H Ph),
6.48 (br, 1H, p-H Ph), 6.22 (br, 2H, o-H Ph), 2.79 (m, 2H, α-H Py), 2.63 (m, 2H,
NCH2-bridge), 2.60 (d, 2H, JHH = 11.9 Hz, CCH2), 2.58 (m, 2H, α-H Py), 2.49 (m, 2H,
NCH2-bridge), 2.30 (m, 2H, NCH2), 2.13 (d, 2H, JHH = 11.9 Hz, CCH2), 2.09 (m, 2H, NCH2),
2.06 (s, 6H, NCH3), 1.65 (m, 4H, β-H Py), 1.64 (br, 2H, YCH2), 0.59 (s, 3H, CCH3). {1H}13C
NMR (125.7 MHz, C6D5Br, 25 ˚C) δ: 153.4 (ipso-C Ph), 133.4 (m-C, Ph), 148.5 (d, JCF =
240.7 Hz, o-C C6F5), 138.3 (d, JCF = 235.0 Hz, p-C C6F5), 136.5 (d, JCF = 242.9 Hz, m-C
C6F5), 124.2 (br, ipso-C C6F5), 118.9 (o-C Ph), 118.3 (p-C Ph), 75.7 (CCH2), 59.4
(NCH2-bridge), 56.8 (CCH3), 56.2 (NCH2), 53.7 (br, YCH2), 52.4 (α-C Py), 48.9 (NCH3),
45.1 (NCH2-bridge), 22.8 (β-C Py), 19.2 (CCH3).
[(L6)LaCH2Ph][B(C6F5)4]. 1H NMR (500 MHz, C6D5Br, 23 ˚C) δ: 6.96 (t, 1H, JHH = 7.2
Hz, p-H Ph), 6.37 (t, 2H, JHH = 7.05 Hz, m-H Ph), 6.21 (d, 2H, JHH = 5.92 Hz, o-H Ph), 2.63
(m, 4H, NCH2-bridge), 2.63 (d, 2H, JHH = 12.7 Hz, CCH2), 2.61 (m, 2H, α-H Py), 2.43 (m,
2H, α-H Py), 2.29 (m, 2H, NCH2), 2.12 (s, 6H, NCH3), 2.10 (d, 2H, JHH = 11.9 Hz, CCH2),
2.02 (m, 2H, NCH2), 1.94 (br, 2H, LaCH2), 1.67 (m, 2H, β-H Py), 1.63 (m, 2H, β-H Py), 0.59
(s, 3H, CCH3). {1H}13C NMR (125.7 MHz, C6D5Br, 23 ˚C) δ 148.5 (d, JCF = 240.7 Hz, o-C
C6F5), 138.3 (d, JCF = 235.0 Hz, p-C C6F5), 136.5 (d, JCF = 242.9 Hz, m-C C6F5), 132.1 (m-C,
Ph), 124.2 (br, ipso-C C6F5), 119.5 (o-C Ph), 114.8 (p-C Ph), 73.9 (CCH2), 63.1 (LaCH2),
59.1 (CCH3), 57.7 (NCH2-bridge), 56.7 (NCH2), 52.3 (α-C Py), 48.9 (NCH3), 46.7
(NCH2-bridge), 23.0 (β-C Py), 20.0 (CCH3). The ipso-C resonance is obscured by the solvent
peaks. 19F NMR (470 MHz, C6D5Br, 23 ˚C) δ -137.1 (d, JFF = 11.5 Hz, o-F), -167.3 (t, JFF =
21.3 Hz, m-F), -171.2 (t, JFF = 17.8 Hz, p-F).
[(L8)ScCH2Ph][B(C6F5)4]. 1H NMR (500 MHz, C6D5Br) δ: 7.05 (t, 2H, JHH = 7.2 Hz,
m-H Ph), 6.67 (t, 1H, JHH = 7.5 Hz, p-H Py), 6.21 (d, 2H, JHH = 6.7 Hz, o-H Ph), 2.99 (m,
2H, α-H Py), 2.68 (m, 2H, α-H Py), 2.37 (d, 2H, JHH = 11.9 Hz, CCH2), 2.19 (d, 2H, JHH =
11.9 Hz, CCH2), 2.07 (br, 4H, NCH2), 2.03 (s, 6H, NCH3), 1.93 (s, ScCH2), 1.73 (m,2H, β-H
Py), 1.56 (m, 2H, β-H Py), 0.48 (s, 3H, CCH3), 0.06 (s, 6H, Si(CH3)2). 13C{1H} NMR (125.6
MHz, C6D5Br) δ: 153.0 (ipso-C Ph), 148.5 (d, JCF = 240.7 Hz, o-C C6F5), 138.3 (d, JCF =
235.0 Hz, p-C C6F5), 136.5 (d, JCF = 242.9 Hz, m-C C6F5), 134.3 (m-C Ph), 124.2 (br, ipso-C
C6F5), 120.8 (p-C Ph), 120.4 (o-C Ph), 80.2 (CCH2), 58.6 (LaCH2), 56.0 (NCH2), 55.8
(CCH3), 50.1 (NCH3), 49.0 (α-C Py), 25.5 (β-C Py), 23.0 (CCH3), 1.56 (Si(CH3)2).
[(L8)YCH2Ph][B(C6F5)4]. 1H NMR (500 MHz, C6D5Br) δ: 6.37 (t, 2H, JHH = 7.4 Hz, m-H
Ph), 5.81 (t, 1H, JHH = 6.6 Hz, p-H Ph), 5.49 (d, 2H, JHH = 7.8 Hz, o-H Ph), 2.77 (m, 2H, α-H
Py), 2.64 (s, 2H, YCH2), 2.33 (d, 2H, JHH = 12.4 Hz, CCH2), 2.31 (m, 2H, NCH2), 2.16 (d, 2H,
JHH = 12.4 Hz, CCH2), 2.10 (m, 2H, NCH2), 2.02 (s, 6H, NCH3), 2.04 (m, 2H, α-H Py), 1.49
(m, 4H, β-H Py), 0.62 (s, 3H, CCH3), 0.00 (s, 6H, Si(CH3)2). 13C{1H} NMR (125.6 MHz,
Chapter 5
106
C6D5Br) δ: 151.5 (ipso-C Ph), 148.5 (d, JCF = 240.7 Hz, o-C C6F5), 138.3 (d, JCF = 235.0 Hz,
p-C C6F5), 136.5 (d, JCF = 242.9 Hz, m-C C6F5), 134.2 (m-C Ph), 124.2 (br, ipso-C C6F5),
114.7 (o-C Ph), 103.7 (p-C Ph), 79.9 (CCH2), 70.2 (YCH2), 56.6 (NCH2), 56.0 (CCH3), 49.6
(NCH3), 48.1 (α-C Py), 26.0 (β-C Py), 24.1 (CCH3), 1.78 (Si(CH3)2).
[(L12)ScCH2Ph][B(C6F5)4]. 1H NMR (500 MHz, C6D5Br) δ: 7.15 (2H, Ph overlapped with
solvent resonance), 6.75 (m, 3H, m, p-H Ph), 3.11 (d, 1H, JHH = 14.1 Hz, CCH2), 2.58 (d, 1H,
JHH = 14.9 Hz, CCH2), 2.43 (m, 1H, NCH2), 2.35 (s, 3H, NCH3), 2.18 (s, 3H, NCH3), 2.10 (s,
3H, NCH3), 2.04 (m, 3H, NCH2), 1.86 (d, 1H, JHH = 14.9 Hz, CCH2), 1.85 (d, 1H, JHH = 14.1
Hz, CCH2), 1.81 (br, 2H, ScCH2), 1.17 (s, 9H, C(CH3)3), 0.57 (s, 3H, CCH3), 0.16 (s, 6H,
Si(CH3)2). 13C{1H} NMR (125.6 MHz, C6D5Br) δ: 148.5 (d, JCF = 240.7 Hz, o-C C6F5), 138.3
(d, JCF = 235.0 Hz, p-C C6F5), 136.5 (d, JCF = 242.9 Hz, m-C C6F5), 132.9 (m-C Ph), 124.2 (br,
ipso-C C6F5), 122.3 (o-C Ph), 120.3 (p-C Ph), 71.7 (CCH2), 63.3 (CCH2), 58.5 (NCH2), 58.4
(C(CH3)3), 57.7 (NCH2), 54.9 (ScCH2), 54.5 (CCH3), 50.4 (NCH3), 47.5 (NCH3), 35.3
(C(CH3)3), 30.8 (NCH3), 17.2 (CCH3), 6.8 (Si(CH3)2). The ipso-C resonance is obscured by
the solvent peaks.
[(L12)YCH2Ph][B(C6F5)4]. 1H NMR (500 MHz, C6D5Br) δ: 7.08 (t, 2H, JHH = 7.2 Hz, m-H
Ph), 6.64 (d, 2H, JHH = 7.4 Hz, o-H Ph), 6.59 (t, 1H, JHH = 7.3 Hz, p-H Ph), 3.27 (d, 1H, JHH =
14.5 Hz, CCH2), 2.52 (d, 1H, JHH = 15.2 Hz, CCH2), 2.48 (m, 1H, NCH2), 2.28 (m, 1H,
NCH2), 2.25 (s, 3H, NCH3), 2.08 (s, 3H, NCH3), 2.07 (m, 1H, NCH2), 1.99 (m, 1H, NCH2),
1.92 (s, 3H, NCH3), 1.90 (d, 1H, JHH = 15.2 Hz, CCH2), 1.88 (2H, YCH2, JHH and JYH not
resolved due to overlap), 1.84 (d, 1H, JHH = 14.5 Hz, CCH2), 1.19 (s, 9H, C(CH3)3), 0.58 (s,
3H, CCH3), 0.13 (s, 3H, SiCH3), 0.16 (s, 3H, SiCH3). 13C{1H} NMR (125.6 MHz, C6D5Br) δ:
148.5 (d, JCF = 240.7 Hz, o-C C6F5), 138.3 (d, JCF = 235.0 Hz, p-C C6F5), 136.5 (d, JCF =
242.9 Hz, m-C C6F5), 131.7 (m-C Ph), 124.2 (br, ipso-C C6F5), 121.7 (o-C Ph), 117.6 (p-C
Ph), 72.5 (CCH2), 62.8 (CCH2), 59.1 (C(CH3)3), 57.1 (NCH2), 55.8 (YCH2), 55.1 (NCH2),
52.9 (CCH3), 49.1 (NCH3), 47.5 (NCH3), 35.5 (C(CH3)3), 31.2 (NCH3), 17.6 (CCH3), 7.8
(SiCH3), 7.2 (SiCH3). The ipso-C resonance is obscured by the solvent peaks.
[(L12)LaCH2Ph][B(C6F5)4]. 1H NMR (500 MHz, C6D5Br) δ: 7.02 (br, 2H, m-H Ph), 6.64
(m, 1H, p-H Ph), 6.25 (br, 2H, o-H Ph), 3.42 (d, 1H, JHH = 14.1 Hz, CCH2), 2.70 (m, 1H,
NCH2), 2.59 (d, 1H, JHH = 15.1 Hz, CCH2), 2.49 (m, 1H, NCH2), 2.37 (s, 3H, NCH3), 2.22 (m,
1H, NCH2), 2.04 (m, 1H, NCH2), 2.03 (d, 1H, JHH = 15.1 Hz, CCH2), 2.01 (s, 3H, NCH3),
1.92 (d, 1H, JHH = 14.1 Hz, CCH2), 1.96 (s, 3H, NCH3), 1.87 (br, 2H, LaCH2), 1.16 (s, 9H,
C(CH3)3), 0.67 (s, 3H, CCH3), 0.21 (s, 3H, SiCH3), 0.07 (s, 3H, SiCH3). 13C{1H} NMR
(125.6 MHz, C6D5Br) δ: 148.5 (d, JCF = 240.7 Hz, o-C C6F5), 138.3 (d, JCF = 235.0 Hz, p-C
C6F5), 136.5 (d, JCF = 242.9 Hz, m-C C6F5), 132.3 (m-C Ph), 124.2 (br, ipso-C C6F5), 121.9
(o-C Ph), 121.2 (p-C Ph), 73.2 (CCH2), 65.2 (LaCH2), 63.1 (CCH2), 60.1 (C(CH3)3), 57.4
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
107
(NCH2), 54.3 (NCH2), 53.2 (CCH3), 48.8 (NCH3), 45.7 (NCH3), 34.4 (C(CH3)3), 31.0
(NCH3), 17.8 (CCH3), 8.6 (SiCH3), 7.9 (SiCH3). The ipso-C resonance is obscured by the
solvent peaks.
In situ generation of [(L6)Y(CH2SiMe3)(THF-d8)x][B(C6H5)4] in THF-d8. THF-d8 (0.6
mL) was added to a mixture of 32 (26.8 mg, 52 μmol) and [PhMe2NH][B(C6H5)4] (23.0 mg,
52 μmol) and the resulting suspension was transferred to an NMR tube equipped with a
Teflon Young valve. The mixture was made homogeneous by warming at 50 ºC and analyzed
by NMR spectroscopy, which indicated full conversion to the ionic species, TMS and free
PhNMe2. 1H NMR (500 MHz, THF-d8), δ: 7.28 (br, 8H, o-H Ph), 6.87 (t, 8H, JHH = 7.05 Hz,
m-H Ph), 6.73 (t, 4H, JHH = 6.85 Hz, p-H Ph), 3.05 (m, 2H, NCH2), 2.94 (m, 2H, NCH2), 2.93
(m, 2H, α-H Py), 2.91 (m, 2H, NCH2), 2.91 (d, 2H, JHH = 12.2 Hz, CCH2N), 2.88 (m, 2H, α-H
Py), 2.61 (d, 2H, JHH = 12.2 Hz, CCH2N), 2.58 (m, 2H, NCH2), 2.44 (s, 6H, NCH3), 1.88 (m,
4H, β-H Py), 0.79 (s, 3H, CCH3), -0.07 (s, 18H, Si(CH3)3), -1.25 (s, 2H, YCH2, JYH not
resolved). 13C NMR (125.7 MHz, THF-d8), δ: 166.4 (q, JBC = 49.9 Hz, ipso-C Ph), 132.3 (d,
JCH = 154.0 Hz, o-C Ph), 120.9 (d, JCH = 152.3, m-C Ph), 117.0 (d, JCH = 154.5 Hz, p-C Ph),
77.5 (t, JCH = 136.4 Hz, CCH2), 61.3 (t, JCH = 134.0 Hz, NCH2), 59.1 (s, CCH3), 58.7 (t, JCH =
139.7 Hz, NCH2), 54.2 (t, JCH = 137.1 Hz, α-C Py), 50.9 (q, JCH = 137.1 Hz, NCH3), 47.2 (t,
JCH = 131.5 Hz, NCH2), 28.9 (dt, JCH = 95.7 Hz, JYC = 39.3 Hz, YCH2), 24.6 (t, JCH = 132.5
Hz, β-C Py), 21.4 (q, JCH = 132.5 Hz, CCH3), 5.9 (q, JCH = 115.9 Hz, Si(CH3)3)
Structure Determinations of Compounds 26-31 and 33-39. These measurements were
performed according to the procedure described for 1 in Chapter 2. Crystallographic data and
details of the data collections and structure refinements are listed in Table 5.4 (for 26-28),
Table 5.5 (for 29-31), Table 5.6 (for 33-25), and Table 5.7 (for 36-39).
Chapter 5
108
Table 5.4. Crystal Data and Collection Parameters of Complexes 26-28.
Compound 26 27 28
Formula C28H43N4Sc C28H43N4Y C28H43N4La
Fw 480.63 524.58 574.57
cryst color, habit yellow, platelet yellow, block yellow, block
cryst size (mm) 0.47 0.41 0.11 0.52 0.48 0.15 0.41 0.26 0.13
cryst syst triclinic triclinic triclinic
space group P-1 P-1 P-1
a (Å) 9.2415(16) 9.2345(10) 9.2008(8)
b (Å) 16.471(3) 16.4721(17) 16.3686(15)
c (Å) 17.628(3) 18.0513(19) 18.2607(17)
(deg) 77.115(3) 75.5247(16) 75.3451(15)
(deg) 89.025(3) 88.9232(17) 89.2363(15)
(deg) 82.541(3) 82.6102(17) 82.9433(15)
V (Å3) 2593.4(8) 2636.3(5) 2640.1(4)
Z 4 4 4
calc, g.cm-3 1.231 1.322 1.446
µ(Mo Kα), cm-1 3.07 22.35 16.4
F(000), electrons 1040 1112 1184
θ range (deg) 2.93, 26.02 3.01, 26.37 2.44, 27.49
Index range (h, k, l) ±11, ±20, ±21 -10:11, ±20, ±22 ±11, -20:21, ±23
Min and max transm 0.8558, 0.8955 0.3329, 0.7152 0.5890, 0.8150
no. of reflns collected 19080 20090 22620
no. of reflns collected 9831 10402 11641
no. of reflns with F0 ≥ 4 σ (F0) 7551 7883 9191
wR(F2) 0.1347 0.0851 0.0997
R(F) 0.0499 0.0342 0.0390
weighting a, b 0.0637, 1.4677 0.0445, 0 0.0548, 0
Goof 1.066 1.000 1.002
params refined 601 939 601
min, max resid dens -0.42, 0.45(7) -0.43, 0.69(7) 0.92, 1.80(13)
T (K) 100(1) 100(1) 100(1)
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
109
Table 5.5. Crystal Data and Collection Parameters of Complexes 29-31.
Compound 29 30 31
Formula C28H45N4ScSi C28H45N4SiY C28H45LaN4Si
Fw 510.73 554.68 604.68
cryst color, habit yellow, block yellow, block yellow, block
cryst size (mm) 0.53 0.49 0.47 0.60 0.46 0.39 0.42 0.33 0.21
cryst syst orthorhombic orthorhombic orthorhombic
space group Pca21 Pca21 Pca21
a (Å) 15.1496(11) 15.2796(13) 14.9861(10)
b (Å) 12.7213(10) 12.5299(11) 13.3527(9)
c (Å) 14.6804(11) 14.9250(13) 14.2973(9)
(deg)
(deg)
(deg)
V (Å3) 2829.3(4) 2857.4(4) 2861.0(3)
Z 4 4 4
calc, g.cm-3 1.199 1.289 1.404
µ(Mo Kα), cm-1 3.25 21.05 15.57
F(000), electrons 1104 1176 1248
θ range (deg) 2.51, 28.28 2.73, 28.28 2.49, 28.28
Index range (h, k, l) ±20, ±16, ±19 -19:20, -16:15, ±19 ±19, ±17, ±19
Min and max transm 0.8218, 0.8623 0.2708, 0.440 0.5099, 0.7211
no. of reflns collected 24385 21922 24767
no. of reflns collected 6784 6643 7040
no. of reflns with F0 ≥ 4 σ (F0) 6209 5663 6551
wR(F2) 0.1040 0.0624 0.0649
R(F) 0.0422 0.0283 0.0265
weighting a, b 0.0607, 0.1637 0.0194, 0 0.0381, 0.4139
Goof 1.087 1.051 1.032
params refined 312 313 312
min, max resid dens -0.52, 0.69(7) -0.16, 0.28(3) -0.53, 1.85(9)
T (K) 100(1) 100(1) 100(1)
Chapter 5
110
Table 5.6. Crystal Data and Collection Parameters of Complexes 33-35.
Compound 33 34 35
Formula C29H49N4ScSi C29H49N4SiY C29H49LaN4Si.0.5(C7H8)
Fw 526.78 570.72 666.80
cryst color, habit colorless, platelet colourless, block yellow, block
cryst size (mm) 0.47 0.36 0.19 0.43 0.36 0.29 0.52 0.47 0.39
cryst syst monoclinic triclinic monoclinic
space group P21/n P-1 P21/c
a (Å) 13.3811(11) 12.7447(7) 19.2588(13)
b (Å) 16.4691(14) 15.5965(8) 11.5414(8)
c (Å) 14.0858(12) 16.2455(8) 16.2244(11)
(deg) 78.8972(9)
(deg) 103.3556(14) 76.0094(9) 114.8323(10)
(deg) 78.8217(9)
V (Å3) 3020.2(4) 3037.7(3) 3272.8(4)
Z 4 4 4
calc, g.cm-3 1.158 1.248 1.353
µ(Mo Kα), cm-1 3.06 19.82 13.68
F(000), electrons 1144 1216 1388
θ range (deg) 2.47, 26.37 2.61, 26.37 2.77, 28.28
Index range (h, k, l) ±16, -20:18, ±17 ±15, ±19, -18:20 ±25, ±15, -21:20
Min and max transm 0.8559, 0.9178 0.4164, 0.5628 0.4809, 0.5865
no. of reflns collected 23322 24166 28740
no. of reflns collected 6120 12110 8109
no. of reflns with F0 ≥ 4 σ 4514 9068 7238
wR(F2) 0.1444 0.0929 0.0671
R(F) 0.0552 0.0381 0.0273
weighting a, b 0.0686, 1.9168 0.0482, 0 0.0334, 1.7923
Goof 1.020 1.020 1.079
params refined 325 649 378
min, max resid dens -0.26, 0.73(6) -0.34, 0.67(8) -0.84, 1.80(8)
T (K) 100(1) 100(1) 100(1)
Rare Earth Organometallics with Monoanionic Tetradentate Ligands Derived from the Me3DAPA Moiety
111
Table 5.7. Crystal Data and Collection Parameters of Complexes 36-39.
compound 36 37 38 39
formula C29H49N4ScSi2 C29H49N4Si2Y C35H61N4Si2Sc C35H61N4Si2Y
Fw 554.86 598.81 639.02 682.97
cryst color, habit colorless, platelet colorless, block colorless, block colourless, bolck
cryst size (mm) 0.26 0.22 0.09 0.54 0.43 0.38 0.31 0.30 0.24 0.45 0.40 0.28
cryst syst monoclinic monoclinic orthorhombic monoclinic
space group P21/n P21/c P212121 P21/n
a (Å) 9.2061(9) 9.2965(8) 11.9857(10) 12.8938(15)
b (Å) 15.661(2) 15.769(1) 17.5366(14) 15.9933 (19)
c (Å) 22.531(2) 22.846(2) 18.3880(15) 18.311(2)
(deg)
(deg) 101.001(2) 101.757(1) 92.968(2)
(deg)
V (Å3) 3188.8(6) 3278.9(5) 3864.9(5) 3770.8(8)
Z 4 4 4 4
calc, g.cm-3 1.156 1.213 1.098 1.203
µ(Mo Kα), cm-1 3.29 18.74 27.9 16.38
F(000), electrons 1200 1272 1392 1464
θ range (deg) 2.27, 25.68 2.58, 28.28 2.47, 25.68 2.36, 27.52
Index range (h, k, l) ±11, -19:18, ±27 -11:12, -21:20, ±30 ±16, ±20, -20:23 ±16, ±20, -20:23
Min and max transm 0.9080, 0.9745 0.3939, 0.4961 0.9184, 0.9360 0.5261, 0.6570
no. of reflns collected 23606 29354 33563 31857
no. of reflns collected 6009 8045 8897 8633
no. of reflns with F0 ≥
4 σ (F0)
3465 6596 6667 5993
wR(F2) 0.1196 0.0746 0.1197 0.1123
R(F) 0.0540 0.0297 0.0539 0.0463
weighting a, b 0.0359, 0 0.0415, 0.5284 0.0567, 0.0 0.0557, 0.2779
Goof 0.987 1.030 1.015 1.021
params refined 521 521 379 374
min, max resid dens -0.46, 0.35(8) -0.24, 0.48(6) -0.23, 0.45(10) -0.39, 0.86(10)
T (K) 100(1) 100(1) 100(1) 100(1)
Chapter 5
112
5.6 References
1. (a) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2001,
637. (b) Bambirra, S.; Meetsma, A.; Hessen, B.; Bruins, A. P. Organometallics 2006, 25, 3486.
(c) Bambirra, S.; van Leusen, D.; Tazelaar, C. G. J.; Meetsma, A.; Hessen, B. Organometallics
2007, 26, 1014.
2. Sc, Lu: (a) Meyer, N.; Roesky, P. W.; Bambirra, S.; Meetsma, A; Hessen, B.; Saliu, K.; Takats, J.
Organometallics 2008, 27, 1501. Sc: (b) Carver, C. T.; Montreal, M. J.; Diaconescu, P. L.
Organometallics 2008, 27, 363. La: (c) Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics,
2006, 25, 3454.
3. (a) Tazelaar, C. G. J.; Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H.
Organometallics 2004, 23, 936. (b) Bambirra, S.; Perazzolo, F.; Boot, S. J.; Sciarone, T. J. J.;
Meetsma, A.; Hessen, B. Orgaometallics 2008, 27, 704.
4. Bambirra, S.; Boot, S. J.; van. Leusen, D.; Meetsma, A.; Hessen, B. Organometallics 2004, 23,
1891.
5. Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973, 126.
6. (a) Mu, Y.; Piers, W. E.; MacQuarrie, D. C.; Zaworotko, M. J.; Young, V. G. Organometallics
1996, 15, 2720. (b) Hultzsch, K. C.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 1999, 38,
227. (c) Emslie, D. J. H.; Piers, W. E.; Parvez, M.; McDonald, R. Organometallics 2002, 21,
4226.
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
113
Chapter 6 Catalytic Dimerization of Terminal Alkynes by
Rare Earth Metal Benzyl Complexes
6.1 Introduction
The catalytic dimerization of terminal alkynes is a straightforward and atom-economical
method to synthesize conjugated enyne motifs, which are important building blocks for
organic synthesis and key units found in a variety of biologically active compounds and
synthetic conjugated polymers for optoelectronic applications.1 Many organometallic
catalysts, employing early2 or late transition metals3 or rare earth metals,4 have been
reported to catalyze this reaction. Nevertheless, it is difficult to find catalysts that can
combine high catalyst activity, selectivity, and broad substrate scope. Organo rare earth
metal catalysts show good activities, but heteroatom-containing substrates have barely been
investigated.5 Although these metals are hard Lewis acids, the high kinetic lability of their
complexes provides interesting opportunities for the conversion of functionalized
substrates.6 Furthermore, little is known about how the performance of these catalysts is
influenced by the metal ionic radius (a uniquely tunable parameter for the trivalent rare
earth metals7), the ancillary ligands, and the use of neutral vs cationic catalyst species for
this transformation.
Catalytic dimerization of terminal alkynes generally takes place in either head-to-head
(linear) or head-to-tail (branched) fashion; the head-to-head dimerization can produce two
linear isomeric butenynes (Z and E) and the head-to-tail dimerization produces the geminal
(gem) isomer (Scheme 6-1). The formation of E- and gem-dimers (pathway A for E-dimer;
pathway B for gem-dimer) involves the generation of an M-C≡CR acetylide moiety
followed by the migratory insertion of an alkyne to yield the alkenyl intermediates
M-C(R)=C(H)C≡CR (for E-isomer) and M-C(H)=C(R)C≡CR (for gem-isomer);
protonolysis of these alkynyl intermediates by an additional alkyne molecule releases the
dimer and regenerates the M-C≡CR species. Rare earth metallocenes have been reported to
catalyze the formation of E and gem-dimer along these two pathways; however, the product
selectivity depends strongly on the substituent R and the size of the metal.4k For example,
for Cp*2LaCH(SiMe3)2-catalyzed dimerization reactions of RC≡CH,4k the gem-enyne is the
major product when R is aliphatic (R = Me, 78%; R = tBu, 100%), whereas the E-enyne is
the major product when R is aromatic (R = Ph, 86% E-dimer + 11% higher oligomers).
When Cp*2YCH(SiMe3)2 (with the smaller metal yttrium) is used to catalyze this
reaction,4k the gem-dimer is obtained as the major product (89%) even for phenylacetylene
(R = Ph), with the E-enyne (11%) as a minor product.
Chapter 6
114
Scheme 6.1. Pathway for Catalytic Dimerization of Terminal Alkynes.
For late transition metal-catalyzed Z-dimer formation in the linear dimerization of
terminal alkynes (Pathway C),8 it is generally accepted that the catalytic cycle starts from
oxidative addition of an alkyne C-H bond to the M-C≡CR moiety to form M(H)(C≡CR)2,
which subsequently isomerizes to a vinylidene species M(=C=CHR)(C≡CR).
Intramolecular attack of the alkynyl ligand onto the α-carbon of the vinylidene ligand
generates the M-alkenyl intermediate M-C(R)=C(H)C≡CR with Z-configuration around the
C=C bond. Protonolysis of the M-alkenyl bond by an additional alkyne molecule then
releases the Z-dimer and regenerates the M-C≡CR species.
Organo actinide and rare earth metal complexes have also been reported to catalyze the
Z-dimer formation;4a,b,9 however, the precise mechanism leading to this Z-selectivity is
unclear. In the dimerization of terminal alkynes catalyzed by the cationic uranium complex
[(Et2N)3U][B(C6H5)4], gem-dimer is formed together with Z-dimer.9 To explain the
formation of the Z-dimer, Eisen et. al. proposed a mechanism involving an
‘insertion/protonolysis’ sequence, but with a fast isomerization of the alkenyl intermediate
E (with a E configuration around the C=C bond) to F (with a Z configuration around the
C=C bond) before protonolysis (Scheme 6.2). Since this isomerization is reversible, it
should never produce only the Z-enyne as the head-to-head dimer, unless the protonolysis
of the U-alkenyl species E is kinetically blocked (i.e. proceeds at a negligible rate).
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
115
Scheme 6.2. Proposed Pathway for Z-dimer Formation by a Cationic Uranium Catalyst.9a,b
Scheme 6.3. Proposed Pathway for Z-selective Alkyne Dimerization by a Cp*-amido Lu
complex.4b
A pathway for Z-dimer formation catalyzed by lanthanide half-metallocene complexes
was proposed by Hou et al.4b This proposed mechanism involves a dimeric alkynyl
complex (with alkynyl groups as the bridging ligands) as the true catalyst (Scheme 6.3).
Coordination of an alkyne to a metal center breaks one of the two alkynyl bridges, and
subsequent stereoselective attack of the terminal alkynyl ligand of the other metal center to
the coordinated alkyne forms the alkenyl intermediate. Protonolysis of the alkenyl
intermediate by an alkyne then releases the Z-dimer and regenerates the dimeric alkynyl
species. This proposal is based on the observation that such dimeric alkynyl complexes
could be isolated. Although a dimeric alkynyl complex can be also observed in the reaction
mixture after complete conversion of the alkyne substrate, its precise role in the catalytic
cycle is not unequivocally proven. It is interesting to note that the isolated dimeric alkynyl
complex only catalyzes the dimerization effectively and with full selectivity to Z-dimer in
the presence of THF. This seems contradictory with the proposed mechanism, as it is
Chapter 6
116
unlikely that the presence of a Lewis base favors the formation of dimers of Lewis acidic
species. In addition, the proposed mechanism thus far has not been substantiated by good
kinetic data. Thus the selective formation of linear Z-dimer in the alkyne dimerization by
non-metallocene rare-earth metal catalysts still awaits a sound explanation.
In this chapter, we describe a comparative study on the dimerization reaction of terminal
alkynes catalyzed by the neutral and cationic scandium, yttrium and lanthanum benzyl
complexes prepared in Chapter 5, to illustrate the effects of metal ion size, ancillary ligand,
and use of neutral vs cationic catalysts on the catalysis. Stoichiometric reactions established
the identity of the reaction intermediates observed during the catalytic substrate conversion.
Based on the reactivity of isolated products from stoichiometric reactions and kinetic
studies on the catalysis, a new reaction scheme is proposed to explain the observed
Z-selectivity for the rare earth metal catalyzed linear dimerization of terminal alkynes.
6.2 Catalytic Dimerization of (Hetero)aromatic Terminal Alkynes by
Neutral and Cationic Rare Earth Metal Benzyl Complexes
6.2.1 Dimerization of Phenylacetylene Catalyzed by Neutral and Cationic Rare Earth Metal Benzyl Complexes
In order to gauge the dependence of catalytic behavior on ion size, ancillary ligand and
complex charge, the various neutral and cationic organo rare earth metal complexes
described in Chapter 5 were screened for activity in the catalytic dimerization of
phenylacetylene. The results are summarized in Table 6.1. None of the neutral scandium
complexes (26, 29, and 33) showed catalytic activity towards phenylacetylene (entry 1, 4,
and 7) at 80 ºC. As all the neutral La-complexes showed activity, the effect of the ancillary
ligands can best be compared on this set (L6, entry 3; L8, entry 6; L12, entry 9). Complex 28,
bearing Me3DAPA-Amine ligand L6, shows the highest activity and full conversion was
observed within 10 min at 80 ºC with full selectivity for the Z-dimer (entry 3). For the
lanthanum catalyst 35, bearing the Me4DAPA-Amide ligand L12, two products (81%
Z-dimer and 19% E-dimer) are observed (entry 9). Comparing the catalytic activity of the
scandium, yttrium, and lanthanum complexes bearing the same ancillary ligand L6 (entry
1-3) indicates that the complex with the larger ionic radius shows the higher activity.
All the ionic catalysts in Table 6.1 are in situ generated from the neutral dibenzyl
complexes by reaction with [PhNMe2H][B(C6F5)4] (B). The ionic yttrium catalyst 27/B
(entry 11) shows the highest activity among all the ionic catalysts (entries 10-18) and full
conversion was obtained within 5 min at 80 ºC with full selectivity for Z-dimer. For
cationic scandium systems, no catalytic activity of is observed for 29/B (entry 13) and 33/B
(entry 16); the catalyst 26/B only sluggishly dimerizes phenylacetylene and two products
(52% Z-dimer and 48% head-to-tail gem-dimer) are observed. The combination of
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
117
lanthanum complexes 28 or 31 with B dimerizes phenylacetylene with low efficiency (even
with prolonged reaction time, full conversion could not be reached), but still shows
Z-selectivity (entries 12 and 15). For catalyst 35/B, full phenylacetylene conversion is
obtained within 1h (entry 18), but the selectivity for Z-dimer is only 29% (the other
products are higher oligomers, as seen by GC-MS analysis).
Table 6.1. Catalytic Dimerization of Phenylacetylene by Neutral and Cationic Rare Earth
Metal Benzyl Complexes.a
entry catalyst M L time(min) conv. (%)b Z-dimer select. (%)b
other prod.
1 26 Sc L6 60 0
2 27 Y L6 25 >99 >99
3 28 La L6 10 >99 >99
4 29 Sc L8 60 0
5 30 Y L8 60 32 >99
6 31 La L8 60 37 >99
7 33 Sc L12 60 0
8 34 Y L12 60 0
9 35 La L12 60 75 81 E-dimer
10 26/B Sc L6 60 <5 52 gem-dimer
11 27/B Y L6 5 100 100
12 28/B La L6 30 25 >99
13 29/B Sc L8 60 0
14 30/B Y L8 60 44 >99
15 31/B La L8 60 24 >99
16 33/B Sc L12 60 0
17 34/B Y L12 60 0
18 35/B La L12 60 >99 29 oligomers
19 28/B La L6 130c >99 >99
20 27/B Y L6 600c <5 >99
a Reaction conditions: Complex 26-31 and 33-35 (10 μmol), [PhNMe2H][B(C6F5)4]
activator (B, 10μmol) where appropriate, [M] = 18.2 mM, substrate (0.5 mmol), solvent:
C6D6 (for neutral catalysts) and C6D5Br (for cationic catalysts), 80 ˚C; b Conversion and
product selectivity are determined by in situ 1H NMR spectroscopy; c solvent: THF-d8.
Chapter 6
118
For the cationic lanthanum catalyst 29/B in C6D5Br, its poor solubility combined with
thermal instability (described in Chapter 5) may account for its low catalytic efficiency. To
see whether the efficiency of this catalyst can be enhanced by using the strongly
coordinating solvent THF-d8 (since THF-d8 can improve the solubility and thermal stability
of ionic organo rare earth metal complexes), the dimerization reaction catalyzed by 29/B
was carried out in THF-d8 (entry 19), and full conversion was obtained in 2h at 80 ºC with
full selectivity to Z-dimer. For comparison, the reaction catalyzed by the ionic yttrium
system 28/B was also tested in THF-d8 (entry 20) and it turned out that this catalyst only
sluggishly dimerizes phenylacetylene, but again full selectivity for Z-dimer was obtained.
Thus it appears that THF is a suitable solvent for the ionic organo rare earth catalysts with
larger metals for the dimerization reaction of terminal alkynes (when their limited solubility
and thermal stability in other solvents under reaction conditions does not allow for full
substrate conversion).
Table 6.2. Catalytic Dimerization of (Hetero)aromatic Terminal Alkynes by Cationic
Yttrium Monobenzyl Species.a
a Reaction conditions: (L6)Y(CH2Ph)2 (10 μmol), [PhMe2NH][B(C6F5)4] (10 μmol), [Y] = 18.2 mM,
substrate (0.5 mmol), solvent: C6D5Br, 80 ˚C. b Conversion and product selectivity are determined by
in situ 1H NMR spectroscopy.
entry substrate time (min) conv. (%)b product select.(%)b
1 a <5 100 100
2 b 30 100 100
3 c 10 100 100
4 d <5 100 100
5 e <5 100 100
6 f <5 100 100
7 g 40 100 100
8 h 60 -- --
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
119
6.2.2 Catalytic Dimerization of Terminal Alkynes by the Cationic Yttrium Complex [(L6)YCH2Ph]+
The combination of 27/B was chosen as an ionic catalyst to examine the catalytic
dimerization reaction of various terminal alkynes in C6D5Br solvent and the results are
summarized in Table 6.2. For substrates a-g, the reactions essentially go to completion with
full selectivity for the Z-enyne, and the Lewis basic anisyl, pyrrolyl, or thienyl groups pose
no problems. Only the use of h, with the 2-pyridyl substituent, results in complete
deactivation of the catalyst. Deprotonation reactions and insertion reactions of pyridines
with organo rare-earth compounds are known and might lead to catalyst deactivation.10 In a
10 mmol scale reaction, 2000 equiv of phenylacetylene (a) were converted within 2.5 h to
give 99% isolated yield of pure 1,1'-(1Z)-but-1-en-3-yne-1,4-diyldibenzene. In a 5 mmol
scale reaction, 1000 equiv of 3-ethynylthiophene (e) were converted within 4 h to give pure
3,3'-(1Z)-but-1-en-3-yne-1,4-diyldithiophene as bright yellow crystals in 94% isolated yield
after recrystallization from methanol. Thus, 27/B is a catalyst that provides Z-selective
alkyne dimerization capability at TONs that would allow practical application in synthesis.
6.2.3 Catalytic Dimerization of Terminal Alkynes by Neutral Lanthanum Complex (L6)La(CH2Ph)2
Although the ionic yttrium catalyst 27/B proves to be a highly effective catalyst for
catalytic dimerization of terminal alkynes that combines high regio- and stereoselectivity
(to linear Z-dimer) and broad substrate scope, it requires the isolated yttrium complex 27,
[PhMe2NH][B(C6F5)4] reagent, and bromobenzene as a weakly nucleophilic polar solvent.
For practical applications in synthesis, a simpler catalyst system would be preferable. As
described above, the neutral lanthanum bis(benzyl) complex 28 in benzene is also a highly
effective catalyst for the Z-selective head-to-head dimerization of phenylacetylene. Here we
study this neutral catalyst to screen its substrate scope. A range of (hetero)aromatic terminal
alkynes was tested and the results are summarized in Table 6.3. For the substrates a-f, the
reactions go essentially to completion with full selectivity for the Z-enynes. All of these
dimerization reactions in benzene are homogeneous at 50-80 ˚C except for
3-ethynylthiophene (substrate f), which may possibly account for the relatively long
reaction time needed for completion. A simpler procedure uses in situ generated 28 by
reaction of La(CH2Ph)3(THF)3 and HL6 in C6D6. This can be used directly for the
dimerization reaction (entries 7-10). The presence of THF, liberated in the catalyst
generation, does slow down the catalysis compared with the reaction catalyzed by isolated
compound 28 (entries 1 and 7; entries 5 and 8). Nevertheless, when THF is removed after
generating the catalyst (by simply evaporating the volatiles), there is no significant
difference in catalyst performance between in situ generated and isolated catalysts (entries
1 and 9; entries 5 and 10).
Chapter 6
120
The isolated and in situ generated neutral lanthanum catalysts were both tested for
dimerization reactions on a preparative scale (see experimental section for details). In 10
mmol scale reactions at 80˚C in toluene solvent with either the isolated catalyst 28, or with
the catalyst generated in situ (with THF removal), 1000 equiv of phenylacetylene were
converted to give 92% and 95% isolated yield of pure Z-dimer, respectively. For the in situ
generated catalyst without THF removal, dimerization of phenylacetylene on a 10 mmol
scale (200 equiv) was performed with 94% isolated yield within 1 h at 80 ˚C.
Table 6.3. Catalytic Dimerization of (Hetero)aromatic Terminal Alkynes by a Neutral
Lanthanum Dibenzyl Complex.a
a Reaction condition: (L6)La(CH2Ph)2 (10 μmol), [La] = 18.2 mM, substrate (0.5 mmol),
solvent: C6D6, 50 ˚C; b Conversion and product selectivity are determined by in situ 1H
NMR spectroscopy; c 80 ˚C; d Catalyst was generated in situ by La(CH2Ph)3(THF)3 and
HL6 in C6D6; e THF was removed before substrates were added.
entry substrate time (min) conv. (%)b product select.(%)b
1 a 35 >99 >99
2 b 90c >99 >99
3 c 25c >99 >99
4 d 15c >99 >99
5 e 10 >99 >99
6 f 150 >99 >99
7 a 75d >99 >99
8 e 20d >99 >99
9 a 50d,e >99 >99
10 e 10d,e >99 >99
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
121
6.3. Isolation and Reactivity of Organo Rare Earth Metal Alkynyl
Complexes
As described above, the neutral dibenzyl and cationic monobenzyl yttrium and
lanthanum complexes supported by the Me3DAPA-Amine ligand L6 effectively catalyze the linear dimerization reaction of terminal alkynes with full selectivity to
Z-dimers. To gain information on the true catalyst species and the mechanism leading to such Z-selective dimerization, the stoichiometric reactions of the neutral complexes
26-28 and the cationic species [(L6)MCH2Ph]+ (M = Y and La) with phenylacetylene were carried out. These reactions resulted in a series of well-defined neutral and
cationic rare earth metal alkynyl complexes.
Scheme 6.4. Synthesis of Dialkynyl Complexes 40-42.
6.3.1 Reaction of Complexes 26-28 with Two Equivalents of Phenylacetylene (Formation of Dialkynyl Complexes)
Upon reaction with 2 equiv of phenylacetylene, the scandium dibenzyl complex 26 is
converted to the mononuclear dialkynyl scandium compound (L6)Sc(C≡CPh)2 (40) and the
yttrium and lanthanum dibenzyl complexes 27 and 28 to the binuclear dialkynyl
compounds [(L6)M(C≡CPh)(μ-C≡CPh)]2 (M = Y, 41; M = La, 42). They were obtained as
colorless crystalline materials after crystallization from a toluene/hexane mixture (isolated
yield: 40, 73%; 41, 70%; 42, 66%) (Scheme 6.4). The 13C NMR resonances of M-C(≡C-Ph)
are found at δ 142.1 ppm for 40, 148.4 ppm for 41, and 162.1 ppm for 42. Room
temperature NMR spectra of 41 and 42 in toluene-d8 indicate a Cs symmetrically averaged
structure and lowering the temperature to -50 ˚C results in a decoalescence of the o-Ph 1H
Chapter 6
122
NMR resonance for both 41 and 42, indicating the presence of bridging and terminal
alkynyl groups. The binuclear dialkynyl complexes 41 and 42 are sparsely soluble in
benzene and toluene, but highly soluble in THF. This might be due to cleavage of the
binuclear dialkynyl complexes by the Lewis basic solvent into the monoculear complexes
(L6)M(C≡CPh)2(THF)x. The mononuclear character of (L6)Y(C≡CPh)2(THF-d8)x was
confirmed by the diagnostic doublet resonance of the YC≡C group at δ 149.2 ppm (d, JYC =
52.9 Hz) in the 13C NMR spectrum.
Figure 6.1. Molecular Structure of 6.1. All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 30% probability level.
Compounds 40-42 were characterized by single-crystal X-ray diffraction and their
structures are shown in Figure 6.1 (for 40) and 6.2 (for 41 and 42), with the geometric data
compiled in Table 6.4. The structure determination of 40 at 100 K was complicated by the
occurrence of a low-temperature phase transition, causing splitting of the diffraction peaks.
To avoid this problem, data collection was carried out at 222 K, resulting in successful
structural characterization, but a lower accuracy due to increased thermal motion of the
atoms. The compound 40 features a distorted octahedral metal center and the coordination
sphere is composed of four nitrogens of the ligand L6 and two terminal alkynyl groups with
Sc-C(15)-C(16) = 172.4(3)º and Sc-C(23)-C(24) = 172.3(3)º. Compounds 41 and 42 are
isostructural and only the structure of 41 is explicitly discussed here. Compound 41 is a
centrosymmetric dimer with two alkynyl groups bridging the two yttrium centers. The core
of the structure is a 4-membered ring Y-C(23)-Y(_a)-C(23_a), which is essentially planar
(the torsion angle Y-C(23)-Y(_a)-C(23_a) is 0.00(12)˚). The Me3DAPA-Amine and
terminal alkynyl ligands in 41 adopt a trans-arrangement around the core. A
cis-arrangement of TACN-amide ligands has been reported for a closely related dialkynyl
lanthanum complex {[Me2TACN(CH2)2NtBu]La(C≡CPh)(μ-C≡CPh)}2.2d The bridging
alkynyl groups are asymmetrically bound to the two yttrium centers, with Y-C(23) =
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
123
2.530(5) Å and Y-C(23)-C(24) = 133.1.(4)˚ vs Y(_a)-C(23) = 2.701(4) Å and
Y(_a)-C(23)-C(24) = 113.1(3)˚. The geometry around the α-carbon (Y-C≡CPh) of the
bridging alkynyl group is slightly distorted from planarity (the sum of angles around C(23)
is 350.0˚). The binding mode of terminal alkynyl groups deviates only slightly from
linearity with Y-C(15)-C(16) = 172.3(4)˚. There is no significant difference in CC triple
bond lengths between terminal and bridging alkynyl groups in 41 and 42.
Figure 6.2. Molecular Structures of 41 (left) and 42 (right). All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Table 6.4. Geometric Data for Complexes 40-41.
40 (M = Sc) 41 (M = Y) 42 (M = La)
M-N(1) 2.485(2) 2.680(3) 2.850(4)
M-N(2) 2.373(3) 2.609(4) 2.730(3)
M-N(3) 2.045(2) 2.223(3) 2.339(3)
M-N(4) 2.333(3) 2.609(4) 2.781(4)
M-C(15) 2.262(3) 2.456(4) 2.670(4)
M-C(23) 2.296(4) 2.530(3) 2.637(4)
M-C(15_a) 2.779(4)
M-C(23_a) 2.701(4)
C(15)-C(16) 1.208(5) 1.212(5) 1.225(6)
C(23)-C(24) 1.214(5) 1.223(6) 1.219(6)
M-C(15)-C(16) 172.4(3) 172.3(4) 134.7(3)
M(_a)-C(15)-C(16) 112.8(3)
M-C(23)-C(24) 172.3(3) 133.1(4) 172.0(4)
M(_a)-C(23)-C(24) 113.1(3)
C(15)-C(16)-C(17) 178.7(3) 174.8(5) 179.2(4)
C(23)-C(24)-C(25) 176.8(4) 179.6(4) 176.3(5)
Chapter 6
124
6.3.2 Reaction of Complexes 26-28 with Three Equivalents of Phenylacetylene (Formation of Trialkynyl Complexes)
Reaction of complexes 26 and 27 with three equiv of phenylacetylene in benzene
afforded the corresponding mononuclear trialkynyl complexes (HL6)M(C≡CPh)3 (M = Sc,
43; M = Y, 44) (Scheme 6.5), by protonation of the two M-benzyl bonds (liberating toluene)
and protonation of the M-amido bond to generate a coordinated secondary amine. They
were isolated as colorless crystalline solids after crystallization from a benzene/hexane (for
43) or THF/hexane (for 44) mixture (isolated yield: 43, 77%; 44, 83%). The yttrium
trialkynyl complex 44 is stable either in the solid state or in benzene or THF solution at
ambient temperature. Its 1H NMR spectrum in THF-d8 reveals a fully asymmetric structure,
as seen by two methyl resonances (δ 2.95 and 2.91 ppm) for the two NCH3 groups and four
resonances (δ 3.75, 3.40, 2.77, and 2.56 ppm) for the four protons of the CH2CH2 bridge.
The pendant pyrrolidinyl group is tightly bound to the yttrium center in THF on the NMR
time scale, as its α-H resonances are diastereotopic at ambient temperature. The resonance
of NH is found at δ 3.74 ppm. Its 13C NMR spectrum at ambient temperature shows a broad
resonance at δ 147.0 ppm for the three Y-C≡C groups, indicating fluxionality. Lowering the
temperature to -50 ºC slows down this dynamic process and three 13C NMR resonances are
observed at δ 150.0 ppm (d, JYC = 51.4 Hz), 148.6 ppm (d, JYC = 47.7 Hz), and 147.8 ppm
(d, JYC = 50.6 Hz) for the three Y-C≡C groups.
Scheme 6.5. Synthesis of Scandium and Yttrium Trialkynyl Complexes.
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
125
Figure 6.3. Molecular structure of 43. Hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Figure 6.4. Molecular structure of 44. Hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
The structures of complexes 43 and 44 were established by single-crystal X-ray
diffraction and their structures are shown in Figure 6.3 and 6.4, respectively, with the
geometric data listed in Table 6.5. Complex 43 features a 6-coordinated scandium center in
an approximately octahedral geometry, with the coordination sphere composed of three of
the four nitrogen atoms of ligand L6 (the pendant pyrrolidinyl group does not bind to the
scandium center) and three terminal alkynyl groups. The three Sc-N bond lengths do not
differ significantly and are within in the normal range of Sc-N(amine) bond lengths,11
indicative of protonation of the Sc-N(amido) bond in dibenzyl complex 26 by
Chapter 6
126
phenylacetylene. The bonding mode of the three alkynyl groups deviates only slightly from
linearity with Sc-C≡C angles of 172.93-174.48(19)º. The structure of 44 reveals a
compound with a 7-coordinated yttrium center with the coordination sphere composed of
four nitrogen atoms of neutral ligand HL6 and three terminal alkynyl ligands. The four Y-N
bond distances range from 2.522(2) Å to 2.618(3) Å, which are in the typical range of
Y-N(amine) distances,12 indicative of tetraamino ligand character. Two alkynyl ligands bind
to the yttrium center in an essentially linear fashion with Y(1)-C(15)-C(16) and
Y(1)-C(23)-C(24) angles of 175.4(3)º and 173.4(3)º, respectively. The coordination mode
of the third alkynyl group deviates significantly from linearity with Y(1)-C(31)-C(32) angle
of 151.2(3)º.
Table 6.5. Geometric Data for 43 and 44.
43 44
Sc(1)-N(11) 2.3609(19) Y(1)-N(1) 2.533(3)
Sc(1)-N(12) 2.3817(19) Y(1)-N(2) 2.597(3)
Sc(1)-N(13) 2.334(2) Y(1)-N(3) 2.522(2)
Sc(1)-N(14) Y(1)-N(4) 2.618(3)
Sc(1)-C(115) 2.240(2) Y(1)-C(15) 2.467(3)
Sc(1)-C(123) 2.250(2) Y(1)-C(23) 2.460(3)
Sc(1)-C(131) 2.259(3) Y(1)-C(31) 2.458(3)
C(115)-C(116) 1.223(3) C(15)-C(16) 1.223(4)
C(123)-C(124) 1.213(3) C(23)-C(24) 1.223(4)
C(131)-C(132) 1.221(3) C(31)-C(32) 1.208(4)
Sc(1)-C(115)-C(116) 174.48(19) Y(1)-C(15)-C(16) 174.5(3)
Sc(1)-C(123)-C(124) 172.93(19) Y(1)-C(23)-C(24) 173.4(3)
Sc(1)-C(131)-C(132) 173.00(19) Y(1)-C(31)-C(32) 151.2(3)
C(115)-C(116)-C(117) 175.7(2) C(15)-C(16)-C(17) 176.9(4)
C(123)-C(124)-C(125) 177.5(2) C(23)-C(24)-C(25) 175.8(4)
C(131)-C(132)-C(133) 178.1(3) C(31)-C(32)-C(33) 169.2(4)
Reaction of lanthanum dibenzyl complex 28 with 3 equiv of phenylacetylene was carried
out on an NMR-tube scale in C6D6 at room temperature and this afforded the binuclear
dialkynyl complex 42 and 0.5 equiv of Z-dimer of phenylacetylene with liberation of 2
equiv of toluene. When this reaction was performed in THF-d8, it afforded a single
organometallic species with concomitant release of 2 equiv of toluene. The same lanthanum
species is formed in the reaction of the binuclear dialkynyl complex 42 with 1 equiv (per
lanthanum) of phenylacetylene in THF-d8. The resulting La-species was characterized by
NMR spectroscopy and was tentatively formulated as (HL6)La(C≡CPh)3 (45).
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
127
6.3.3 Cationic Yttrium and Lanthanum Alkynyl Species
Upon reaction with 1 equiv of [PhNMe2H][B(C6F5)4] in THF-d8, (L6)M(CH2Ph)2 (M = Y
and La) were cleanly converted to the cationic monobenzyl species
[(L6)M(CH2Ph)(THF-d8)x]+. Subsequent treating these in-situ generated cationic species
with 1 equiv of phenylacetylene (per metal) afforded cationic alkynyl species
[(L6)M(C≡CPh)(THF-d8)x]+. These cationic species were characterized by NMR
spectroscopy; the 13C NMR resonance of the M-C≡C group is found at δ 144.5 ppm (d, JYC
= 53.2 Hz) for [(L6)Y(C≡CPh)(THF-d8)x]+ and δ 160.5 ppm for
[(L6)La(C≡CPh)(THF-d8)x]+.
Reaction of the binuclear dialkynyl yttrium complex 41 with 1 equiv (per yttrium) of
[PhNMe2H][B(C6F5)4] was performed on an NMR-tube scale in THF-d8. This reaction
afforded a single yttrium species, but its 1H NMR spectrum does not match the 1H NMR
spectrum of [(L6)Y(C≡CPh)(THF-d8)x]+; furthermore no liberated phenylacetylene was
observed. The same yttrium species is obtained when the in situ generated monoalkynyl
species [(L6)Y(C≡CPh)(THF-d8)x][B(C6F5)4] is reacted with 1 equiv of phenylacetylene. A
single-crystal X-ray study on the isolated material (Figure 6.5, the geometric data listed in
Table 6.6) showed that the yttrium species can be formulated as [(HL6)Y(C≡CPh)2(THF)]+
(Scheme 6.6). On a preparative scale, it was obtained as a colorless crystalline solid
(isolated yield: 83%) as its tetraphenylborate salt [(HL6)Y(C≡CPh)2(THF)][BPh4] (46) by
reaction of the dibenzyl yttrium complex 27, 2 equiv of phenylacetylene, and 1 equiv of
[PhNMe2H][B(C6H5)4] in THF (Scheme 6.6), followed by recrystallization from a
THF/toluene mixture. Its solution 1H NMR spectrum in THF-d8 shows a fully asymmetric
structure, as seen by two methyl resonances (δ 2.99 and 2.75 ppm) for the NCH3 groups
and four resonances (δ 4.20, 3.68, 3.50, and 3.06 ppm) for the four α-H of the pyrrolidinyl
group. The NH resonance is found at δ 3.94 ppm (dd, JHH = 11.8 Hz, and JHH = 4.3 Hz).
The 13C NMR resonances of the two Y-C≡C groups are found at δ 144.9 ppm (d, JYC = 51.3
Hz) and 144.2 ppm (d, JYC = 53.0 Hz), indicative of the mononuclear character of this
species.
Scheme 6.6. Synthesis of an Ionic Dialkynyl Yttrium Complex 46.
Chapter 6
128
The structure of 46 reveals a cation with a 7-coordinated yttrium center, and the
coordination sphere is composed of four nitrogen atoms of ligand HL6, one THF and two
terminal alkynyl ligands. The four Y-N bond distances (2.494(4)-2.567(4) Å) are in the
range of Y-N(amine) bond distances,12 indicative of tetraamine ligand character. The
binding mode of the two alkynyl ligands deviates only slightly from linearity with
Y(11)-C(115)-C(116) and Y(11)-C(123)-C(124) angles of 172.7(5)º and 178.4(5)º,
respectively.
Figure 6.5. Molecular Structure of 46. All hydrogen atoms and the anion [B(C6H5)4]-
are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Table 6.6. Selected Geometrical Data of Complex 46.
Bond lengths (Å)
Y(11)-N(11) 2.567(4) Y(11)-C(115) 2.419(6) Y(11)-N(12) 2.535(4) Y(11)-C(123) 2.425(6)
Y(11)-N(13) 2.494(4) C(115)-C(116) 1.228(8) Y(11)-N(14) 2.555(4) C(123)-C(124) 1.218(8)
Y(11)-O(11) 2.419(4) Bond angles (deg)
Y(11)-C(115)-C(116) 172.7(5) C(115)-C(116)-C(117) 175.4(6) Y(11)-C(123)-C(124) 178.4(5) C(123)-C(124)-C(125) 178.3(6)
The cationic dialkynyl lanthanum species [(HL6)La(C≡CPh)2(THF-d8)x][B(C6F5)4] (47)
can be cleanly generated in situ in THF-d8 on NMR tube scale, either by the reaction of the
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
129
monoalkynyl lanthanum species [(L6)La(C≡CPh)(THF-d8)x][B(C6F5)4] with 1 equiv of
phenylacetylene or by the reaction of binuclear dialkynyl lanthanum complex 43 with 1
equiv of [PhNMe2H][B(C6F5)4] (per La). Attempts to isolate it resulted in a sticky solid that
is insoluble in THF; this product has thus far eluded characterization.
Scheme 6.7. Decomposition of the Scandium Trisalkynyl Complex 43.
Scheme 6.8. Thermal Decomposition of Trisalkynyl Yttrium Complex 44.
6.3.4 Thermal Reactivity of Neutral Trisalkynyl Scandium, Yttrium and Lanthanum Complexes
Once the scandium trisalkynyl complex 43 is dissolved in C6D6 at ambient temperature,
it is readily converted back to the dialkynyl complex 40 by losing 1 equiv of
phenylacetylene, as seen by 1H NMR spectroscopy (Scheme 6.7). This is likely to be due to
an intramolecular proton transfer from the coordinated secondary amine NH to the
α-carbon of one of the Sc-C≡C moieties. Thus the addition of phenylacetylene to 40 seems
to be reversible, with the equilibrium lying far to the side of starting materials. No
sequential process leading to C-C coupling between alkynyls (as an intermediate step in
phenylacetylene dimerization) could be observed. Subsequently warming the solution to 50
ºC also does not result in the coupling of the alkynyl groups.
When the yttrium trisalkynyl complex 44 is dissolved in C6D6 at ambient temperature, it
is only partially converted back to the dialkynyl complex 41 (about 8%, as determined by 1H NMR spectroscopy), indicating an equilibrium between the trisalkynyl complex 44 and
Chapter 6
130
the dialkynyl complex 41 plus free phenylacetylene, that lies on the side of the product 44.
Subsequent warming of the solution at 50 ºC results in complete conversion to the
dialkynyl complex 41 with concomitant liberation of 0.5 equiv of Z-dimer, as shown in
Scheme 6.8. The same reactivity is observed for 44 in THF-d8, but the yttrium dialkynyl
complex is a mononuclear species in this case (see section 6.2.1). The lanthanum
trisalkynyl complex 45 in THF-d8 shows the same reactivity as described for the yttrium
congener 44.
A possible pathway to form the dialkynyl complex 41 and the Z-dimer from the
trisalkynyl complex 44 is depicted in Scheme 6.9. It involves an intermolecular proton
transfer from the NH group of the coordinated secondary amine to the β-carbon of Y-C≡C
moiety (electrophilic attack on the -cloud), which makes the α-carbon of this unit
susceptible to nucleophilic attack from the other side by an alkynyl ligand in its vicinity.
This forms the cationic alkenyl intermediate E (with a Z configuration around the C=C
double bond) and the anionic trisalkynyl intermediate F, as shown in Scheme 6.9.
Subsequent intramolecular protonolysis of the Y-alkenyl bond in E by the NH group of the
ligand releases the Z-dimer and forms the cationic monoalkynyl species G. An alkynyl
ligand redistribution reaction between the anion F and the cation G generates the binuclear
dialkynyl complex 41.
Scheme 6.9. Proposed Pathway for the Z-enyne Formation from Complex 44.
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
131
An unusual feature of this proposed route is the intermolecular electrophilic attack of the
proton of the coordinated secondary amine ligand to an alkynyl -carbon. Nevertheless,
tandem electrophilic-nucleophilic attack on C≡C bonds is well-precedented13 and it offers a
few attractive features: it provides an explanation for the Z-configuration around the double
bond of the enyne formed (electrophile and nucleophile attack from opposite sides), and it
involves a reaction step where two metal centers are involved (for which kinetic evidence is
available, see below). A direct intramolecular attack of the NH proton on the alkynyl
-carbon is unlikely: the shortest distance between the proton and an alkynyl -carbon in
the structure of 44 is 3.7 Å.
6.3.5 Reactivity of Cationic Dialkynyl Yttrium and Lanthanum Complexes
Once the cationic yttrium dialkynyl complex 46 is dissolved in THF-d8, traces of free
phenylacetylene and the cationic monoalkynyl complex (L6)Y(C≡CPh)(THF-d8)x (< 3%
relative to 46) are observed. Under these conditions no formation of Z-dimer was detected
by 1H NMR spectroscopy. In C6D5Br solvent, complex 46 is thermally labile and releases
0.5 equiv of Z-dimer, although no well-defined organometallic species could be identified
after completion of the reaction. When, during this decomposition, the reaction mixture was
quenched with D2O, subsequent 1H NMR and GC-MS analyses indicate the formation of an
appreciable amount of the monodeuterated Z-dimer (PhC≡C)CD=C(H)Ph. Formation of
this particular isotopomer shows that the yttrium is bound to the alkenyl carbon bearing the
alkynyl group in a Y-C(-C≡CPh)=C(H)Ph species after the C-C bond formation step has
occurred. This is a marked contrast with the proposed dimerization mechanism by Hou et.
al. (shown in Scheme 6.3) where a different metal alkenyl isomer, M-C(Ph)=CH(-C≡CPh),
is formed before the protonolysis step occurs.
The cationic yttrium and lanthanum dialkynyl complexes 46 and 47 show the same
reactivity in THF-d8 and only the reactivity of the yttrium complex 46 is explicitly
discussed here. When the solution of 46 in THF-d8 is warmed at 80 ºC, it is converted to the
cationic monoalkynyl yttrium species (L6)Y(C≡CPh)(THF-d8)x with concomitant liberation
of 0.5 equiv of Z-dimer. A possible pathway for this process is depicted in Scheme 6.10 and
it is similar to the one proposed for the Z-dimer formation process from the neutral yttrium
trisalkynyl complex 44 in Scheme 6.9. The intermolecular proton transfer from the
coordinated NH to the β-carbon of Y-C≡C moiety, followed by the nucleophlic attack on
the α-carbon of this unit by the other alkynyl group, forms the dicationic yttrium alkenyl
intermediate {(HL6)Y[-C(C≡CPh)=C(H)Ph](THF-d8)x}2+ (I) and the neutral dialkynyl
yttrium complex (L6)Y(C≡CPh)2(THF-d8)x (H). Subsequent intramolecular protonolysis of
the Y-alkenyl bond by the coordinated NH in I releases the Z-dimer and generates the
dicationic yttrium species [(L6)Y(THF-d8)x]2+. The last step is the ligand redistribution
reaction between the dicationic species [(L6)Y(THF-d8)x]2+ with the neutral dialkynyl
complex (L6)Y(C≡CPh)2(THF-d8)x, affording the cationic monoalkynyl yttrium species
Chapter 6
132
[(L6)Y(C≡CPh)(THF-d8)x]+. To test the possibility of such a ligand redistribution reaction,
the dicationic species [(L6)Y(THF-d8)x]2+
(generated in situ by reaction of the yttrium
dibenzyl complex 27 with 2 equiv of [PhNMe2H][B(C6F5)4] in THF-d8) was reacted with
0.5 equiv of the binuclear yttrium dialkynyl complex 41 in THF-d8. The 1H NMR spectra of
the reaction mixture indicated a rapid and clean formation of [(L6)Y(C≡CPh)(THF-d8)x]+.
Scheme 6.10. Z-enyne Formation from the Cationic Dialkynyl Complex 46 in THF-d8; the
THF-d8 molecules coordinated to the yttrium center and [B(C6H5)4]- are omitted for clarity.
6.4 Mechanistic Aspects of Catalytic Alkyne Dimerization by Neutral
and Cationic Rare Earth Metal Catalysts
6.4.1 Kinetic Study of Catalytic Dimerization of Phenylacetylene by Neutral and Cationic Catalysts
The kinetics of the catalytic dimerization of phenylacetylene by the two most active
catalyst systems, the ionic yttrium system 27/[PhNMe2H][B(C6F5)4] in C6D5Br and the
neutral lanthanum system 28 in C6D6, were studied. Plots of the substrate conversion versus
time are shown in Figure 6.6. The catalysis by the ionic yttrium system shows a zero-order
dependence on substrate concentration over the entire conversion range. The neutral
lanthanum system shows a zero-order dependence on the substrate concentration only over
the first 50% conversion, suggesting a change in the rate determining step at lower
substrate concentration.
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
133
The relatively poor solubility of the ionic yttrium catalyst system in C6D5Br precludes a
study of the reaction rate dependence on catalyst concentration over a sufficiently large
concentration range. As described above, the ionic lanthanum catalyst system
28/[PhNMe2H][B(C6F5)4] in THF-d8 also catalyzes the dimerization reaction of
phenylacetylene with full conversion and full selectivity to Z-enyne and the reaction
mixture is homogenous even when the catalyst concentration reaches 50 mM. This offers us
a possibility to study the rate dependence on catalyst concentration. This reaction in THF-d8
also shows a zero order dependence on substrate concentration over the full conversion
range (Figure 6.7, left). A plot of the reaction rate versus the square of the catalyst
concentration, in which substrate concentration is held constant (1.0 M) and the catalyst
concentration is varied, shows the reaction to be second order in catalyst concentration
(Figure 6.7, right). Thus, the empirical rate law of this catalytic reaction can be formulated
as: Rate = k[catalyst]2[substrate]0 (k = 0.415 mol-1Ls-1 when the reaction was performed at
80 ºC; if THF-d8 is involved in the catalysis, its concentration stays constant during
catalysis and can be included in the apparent rate constant k).
Figure 6.6. Dimerization of phenylacetylene with 27/B in C6D5Br at room temperature (left)
and with 28 in C6D6 at 35 ºC (right). The lines are least-squares fits to the data points.
Figure 6.7. Substrate concentration as a function of time for the dimerization of
phenylacetylene catalyzed by 28/B in THF-d8 at 80 ºC (left, [La] = 30 mM); Determination
of reaction order in catalyst concentration in THF-d8: plots of rate versus [catalyst]2 (right).
The lines are least-square fits to the data points.
k = 1.9x10-2 min-1
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40 50 60Time / min
Con
vers
ion
k = 1.58 x 10-2 min-1
0.0
0.2
0.4
0.6
0.8
1.0
0 20 40 60 80 100Time / min
Con
vers
ion
y = -0.0224x + 0.9757
R2 = 0.9985
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40
Time / min
[sub
stra
te]
M
y = 0.0015x - 0.0506
R2 = 0.9972
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 250 500 750 1000 1250 1500
[Catalyst]2 / mM2
Rat
e / M
/h
Chapter 6
134
6.4.2 The Proposed Mechanistic Scheme for Catalytic Dimerization of Terminal Alkynes by Neutral and Cationic Rare Earth Catalysts
The observations made from the stoichiometric reactions of the catalyst metal dibenzyl
catalyst precursors with phenylactetylene, combined with the kinetic investigations, allow
us to make a proposal for the catalytic cycles for the Z-selective head-to-head dimerization
of alkynes. For the dimerization of phenylacetylene catalyzed by the neutral yttrium
complex, the catalyst precursor 27 reacts with phenylacetylene (present in large excess) to
form the trisalkynyl complex 44, which can be observed under catalysis conditions by 1H
NMR spectroscopy. After the substrate is completely consumed, the only organoyttrium
species in the reaction mixture is the dialkynyl complex 41. This, combined with the
above-mentioned reactivity study of the trialkynyl complex 44, can lead to a proposed
reaction scheme as shown in Scheme 6.11 (for the neutral catalyst system). For the product
release step, it cannot be excluded that, in the presence of a large excess of alkyne, the M-C
bond in the alkenyl intermediate may also be protonated by the substrate. A similar reaction
cycle was also proposed for the ionic catalyst system in THF (Scheme 6.12).
Scheme 6.11. The Proposed Cycle for Catalytic Dimerization of Phenylacetylene Catalyzed
by the Neutral Yttrium Catalyst.
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
135
Scheme 6.12. The Proposed Cycle for Catalytic Dimerization of Phenylacetylene Catalyzed
by the Ionic Catalysts in THF-d8 (M = Y and La); the THF-d8 molecules coordinated to the
metal center and [B(C6F5)4]- are omitted for clarity.
In our proposed reaction scheme, the ligand amido nitrogen atom plays an essential role
for this catalytic process. It accepts a proton from the substrate alkyne, and this proton, on a
metal-coordinated secondary amine, then acts as electrophile. In this respect it may be
mentioned that all effective Z-selective linear alkyne dimerization catalysts based on rare
earth metals or actinides either bear one or more amido ligands, or employ secondary amine
additives.4a,b,5b,d,14 To probe the importance of such an amide/secondary amine functionality,
we have designed a new 1,4-diazepan-6-amine based ligand with four tertiary amine
functionalities (L16 from Chapter 2, see Scheme 6.13), by replacing the potentially active
hydrogen in ligand HL6 with a methyl group. With this ligand L16, we can generate a
cationic yttrium dibenzyl catalyst precursor [(L6)Y(CH2Ph-p-Me)2][B(C6F5)4] (48 in
Scheme 6.13), the cation of which is an isoelectronic analogue (14e species) of the neutral
yttrium dibenzyl complex 27, which has proven to be an effective catalyst, with a very
similar coordination environment of the metal.
Chapter 6
136
Scheme 6.13. Neutral Tetradentate Ligand L16 and the Cationic Dibenzyl Complex 48.
The cationic yttrium dibenzyl species 48 was generated in situ according to the following
procedure: Y(CH2Ph-p-Me)3(THF)3 was reacted with the neutral ligand L16 in C6D6,
followed removal of all the volatiles. The resulting material was reacted with 1 equiv of
[PhNMe2H][B(C6F5)4] in C6D5Br. The ionic complex 48 was characterized by 1H and 13C
NMR spectroscopy and its NMR spectra in C6D5Br indicate a fully asymmetric structure as
seen by three methyl resonances for NMe-groups and four proton resonances for the α-H’s
of the pyrrolidinyl group. The latter also shows that the pendant pyrrolidinyl group is bound
to the yttrium center on the NMR time scale. The 1H NMR resonances of the YCH2 groups
are found at δ 1.65 and 1.36 ppm (JHH and JYH not resolved due to overlap) and δ 1.62 and
1.56 ppm (JHH and JYH not resolved due to overlap), with the corresponding 13C{1H} NMR
resonances at δ 55.4 ppm (d, JYC = 25.3 Hz) and δ 58.9 ppm (d, JYC = 41.4 Hz).
The catalytic dimerization of phenylacetylene was attempted with both the cationic
yttrium dibenzyl complex 48 and the neutral yttrium dibenzyl complex 27 under the same
conditions (0.5 mmol phenylacetylene with 10 μmol catalyst in 0.5 mL of C6D5Br at 80 ºC).
Full conversion was obtained for 27 with full selectivity for Z-dimer within 30 min. In stark
contrast, no catalytic activity was observed for 48 over a period of 2 h. This seems to
confirm that the Y-N(amido) bond in the catalyst precursor does play a pivotal role in this
catalytic transformation.
If, as mentioned above, the protonation of the M-N(amido) bond by the substrate is
important for the catalysis, the catalyst might be able to discriminate alkyne substrates with
significantly different acidity, favoring the alkyne with higher acidity when two different
alkynes are employed as substrate. To test this, a dimerization experiment with
phenylacetylene (0.25 mmol) and 1-hexyne (0.25 mmol) as substrates and the lanthanum
dibenzyl complex 28 (10 μmmol) as catalyst was performed in C6D6 (0.6 mL) at 80 ºC and
the reaction was monitored by 1H NMR spectroscopy. Interestingly, the reaction takes place
in two stages; in the first stage, the catalyst only converts phenylacetylene to the
corresponding Z-dimer. When phenylacetylene is fully consumed, the catalyst starts to
dimerize 1-hexyne. It does this at a significantly slower rate (34% conversion is reached in
6 h), but also to a linear dimer with Z-selectivity. No cross-coupling products of
phenylacetylene and 1-hexyene were detected by 1H NMR spectroscopy. The observed
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
137
Z-selective head-to-head dimerization of 1-hexyne is significant, since 1-hexyne has an
electronic preference for 1,2-insertion into a M-C≡C-R moiety, leading to a head-to-tail
gem dimer (see Scheme 6.1 for the pathway of gem-dimer formation). Explaining this
unusual selectivity for linear head-to-head 1-hexyne dimerization requires a different
mechanism than the normal ‘insertion/protonolysis’ mechanism (Scheme 6.1). The
proposed reaction scheme in Scheme 6.11 predicts the linear Z-dimer to be the product for
1-hexyne dimerization as well.
6.4.3. Isomerization between Z- and E-dimers of Phenylacetylene
As mentioned in the introduction, the cationic uranium catalyst system [(Et2N)3U][BPh4]
was proposed to produce the Z-dimer via the classic ‘insertion/protonolysis’ mechanism,9a,b
but with an isomerization of the alkenyl uranium intermediate before protonolysis by the
alkyne substrate, as shown in Scheme 6.2. Nevertheless, this would require an unusual
inertness to protonolysis of one of the U-alkenyl intermediates; otherwise this process
should yield a thermodynamic equilibrium mixture between the Z- and E-isomers. We
observed that, for the catalysts described in this chapter for Z-selective linear dimerization
of terminal alkenes, the Z-dimer can be (slowly) isomerized after all the alkyne substrate is
consumed: after prolonged reaction time a thermodynamic equilibrium mixture of Z- and
E-dimers is reached. Here we take the dimerization of phenylacetylene catalyzed by the
neutral lanthanum dibenzyl catalyst precursor 28 as an example to discuss this
phenomenon.
When a solution of 50 equiv of phenylacetylene (0.5 mmol) in C6D6 (0.5 mL) is warmed
at 80 ºC in the presence of 28, full conversion to Z-dimer is obtained in 10 min. However, if
the mixture is continuously kept at this temperature, E-dimer starts to appear gradually until
it finally reaches an equilibrium with the E:Z-dimer ratio of 3:1. This process is very slow
and it takes a few days at 80 ºC to reach equilibrium. This isomerization takes place only
after the phenylacetylene is completely consumed; at this stage the lanthanum species exists
predominantly in the form of the binuclear dialkynyl complex 43. The isolated complex 43
does not show any reactivity towards the isolated Z-dimer under these conditions; thus it
can be excluded that 43 itself is the catalyst for this isomerization process. It is possible that,
after completion of the dimerization, a fraction of the La-catalyst is present as a La-alkenyl
species. The latter, being more basic, should be able to deprotonate the Z-dimer in solution
and initiate the isomerization. Unfortunately, we have not been able to isolate or
unequivocally observe such an alkenyl intermediate.
When a solution of isolated Z-dimer of phenylacetylene in C6D6 is warmed at 80 ºC,
isomerization of Z-dimer to E-dimer does not take place and this indicates that the
isomerization process does need a catalyst under these conditions. The lanthanum dibenzyl
complex 28 was then employed as catalyst precursor to study this isomerization further.
The isolated Z- or E-dimer (0.25 mmol) in C6D6 (0.5 mL) was treated with 28 (10 μmol, 4
Chapter 6
138
mol %) at 80 ºC as shown in Scheme 6.114. For both reactions, a thermodynamic
equilibrium with the E:Z-dimer ratio of 3:1 was obtained in about an hour. This substantial
rate increase, compared with the above-mentioned very sluggish isomerization after
completion of dimerization reaction, might be due to a greater amount of active species in
the reaction mixture. During this reaction, 2 equiv of toluene per La is released as seen by 1H NMR spectroscopy, indicative of effective H-abstraction from Z- or E-dimer to form
lanthanum alkenyl species. Thus, it seems that the C-H activation of the dimer indeed
initiates the isomerization. Nevertheless, the precise mechanism leading to this
isomerization is unclear as yet. It could involve a process similar to that proposed by Eisen
et al. for the cationic uranium catalyst (Scheme 6.2).
Scheme 6.14. Isomerization between Z- and E-dimer by 28.
6.5. A One-pot Procedure for the Z-selective Catalytic Dimerization of
Terminal Alkynes with {HL6 + La[N(SiMe3)2]3}
As described above, the ionic yttrium catalyst 27/[PhNMe2H][B(C6F5)4] and the neutral
lanthanum catalyst 28 effectively catalyze the Z-selective dimerization of terminal alkynes
with high proven turnover number (2000 for the ionic yttrium catalyst and 1000 for the
neutral lanthanum catalyst) that allows for practical applications; however, this requires the
prior isolation of highly sensitive rare earth metal alkyl complexes or organo rare earth
metal starting material, the use of expensive fluorinated borate reagent (to generate the
cationic active species), or weakly nucleophilic polar solvents, such as bromobenzene. The
observations that phenylacetylene is able to protonate the M-N(amido) bond to form a
M-alkynyl bond and an amine prompted us to study this dimerization reaction using rare
earth metal amide catalyst precursors. The combination of La[N(SiMe3)2]3 with amine
addictives has been reported to catalyze this transformation, but this provides only
moderate efficiency and Z-selectivity.14 Here we use the combination of HL6 and
La[N(SiMe3)2]3 as catalyst for the catalytic dimerization of terminal alkynes.
The protocol for the {HL6 + La[N(SiMe3)2]3} catalyzed dimerization of alkynes,
illustrated for the dimerization of phenylacetylene, is as follows. Phenylacetylene (10 mmol)
was added to a solution of La[N(SiMe3)2]3 (10 μmol) and HL6 (10 μmol) in toluene (0.2 ml).
The mixture was warmed at 100 ˚C for 4 h, after which the volatiles were removed in
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
139
vacuum. Extraction with hexane, passing the extract over a short silica column and
evaporation of the volatiles yielded 0.96 g (4.7 mmol, 94% isolated yield) of pure Z-enyne.
The same reaction protocol without the addition of HL6 did not result in conversion,
showing that the presence of the ligand is essential for the catalysis.
Scheme 6.15. Synthesis of the Lanthanum Bisamide Complex 49.
Figure 6.8. Molecular structure of 49. All the hydrogen atoms are omitted for clarity and
thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and
angles (deg): La-N(1) = 2.773(2), La-N(3) = 2.3333(19), La-N(4) = 2.854(2), La-N(5) =
2.5269(19), La-N(6) = 2.4292(19); N(1)-La-N(3) = 65.57(6), N(1)-La-N(4) = 128.39(6),
N(3)-La-N(4) = 68.18(7), N(5)-La-N(6) = 150.20(6).
We subsequently performed the stoichiometric reaction of HL6 with 1 equiv of
La[N(SiMe3)2]3 in C6D6. This reaction proceeded only very slowly at 80 ºC and only partial
conversion to (L6)La[N(SiMe3)2]2 (49) was obtained (65% after 24 h; prolonged heating at
this temperature leads to concomitant decomposition). The reaction is much cleaner and
gives full conversion to (L6)La[N(SiMe3)2]2 when the reaction is carried out in THF-d8 with
warming at 80 ºC for ~30 h (Scheme 6.15). The slowness of this reaction suggests that,
under catalysis conditions, reaction of La[N(SiMe3)2]3 with phenylacetylene precedes
reaction with HL6 in generating the active catalyst. On a preparative scale, the lanthanum
Chapter 6
140
bisamide complexes 49 was obtained (isolated yield: 86%) as a colorless crystalline solid.
Its structure (Figure 6.8) reveals a 5-coordinated lanthanum center, with the coordination
sphere composed of two amide groups and three nitrogen atoms of ligand L6, in which one
of the nitrogen atoms of the 1,4-diazepane moiety is not bound to the metal.
Table 6.3. Catalytic Dimerization of (Hetero)aromatic Terminal Alkynes by {HL6 +
La[N(SiMe3)2]3}.
Reaction condition: a La[N(SiMe3)2]3 (10 μmol), HL (10 μmol), [La] = 18.2 mM,
substrate (0.5 mmol), solvent: C6D6 (0.5 ml), 50 ˚C. b 28 (10 μmol), substrate (0.5 mmol),
solvent: C6D6 (0.5 ml), 50 ˚C. c 49 (10 μmol), substrate (0.5 mmol), solvent: C6D6 (0.5 ml),
50 ˚C; d Conversion and product selectivity are determined by in situ 1H NMR spectroscopy. e 80 ˚C.
The catalytic dimerization of a range of (hetero)aromatic alkynes (a-f) was studied on
NMR tube scale using La[N(SiMe3)2]3 + HL6 and the results are summarized in Table 6.7
(the results for isolated 28 are juxtaposed for easy comparison). For all substrates, complete
conversion with full selectivity to the Z-enyne was observed. Differences in the rate of the
entry substrate time (min) conv. (%)d product select.(%)d
1 a 30a
35b >99 >99
2 b 75a
90b >99e >99
3 c 30a
25b >99e >99
4 d 15a
15b >99e >99
5 e 10a 10b
>99 >99
6 f 170a
150b >99 >99
7 a 35c >99 >99
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
141
catalysis by La[N(SiMe3)2]3 + HL6 and isolated 28 are very small, suggesting that the same
catalytically active species is operative in both cases. The steric hindrance of ortho
substituents slows the catalysis somewhat, but not dramatically. The slowest conversion is
seen for 3-ethynylthiophene (f). It appears that this reaction mixture is not completely
homogeneous during catalysis, which may account for this. The isolated bisamide complex
49 dimerizes phenylacetylene (a) at a rate identical to that of the in situ generated catalyst.
6.6 Concluding Remarks
Neutral dibenzyl and cationic monobenzyl yttrium and lanthanum complexes, supported
by the monoanionic tetradentate 1,4-diazepan-6-amine based ligands L6, L8, and L12, are
active in the catalytic dimerization of terminal alkynes; the cationic (L6)-Y and the neutral
(L6)-La catalysts are the most effective for Z-selective head-to-head dimerization, with a
high tolerance for heteroatom-containing substrates. They show significantly higher
turnover frequency (up to 800 TO h-1) than other catalysts for this transformation,4a,b,14 and
were successfully applied on a preparative scale with proven turnover numbers up to 2000
(for the cationic (L6)-Y catalyst) and 1000 (for the neutral (L6)-La catalyst). For practical
application in the catalytic synthesis of Z-enynes, the neutral (L6)-La system is the most
convenient, as it obviates the use of an expensive fluorinated borate cocatalyst and a
weakly nucleophilic polar solvent like bromobenzene; most interestingly, it can be applied
in the one-pot preparation of Z-enynes with the facile in situ catalyst generation from HL6
and La[N(SiMe3)2]3, which is commercially available or easy to generate from La-trihalides
and Na[N(SiMe3)2].17
Based on the kinetics of the catalytic alkyne dimerization, on observations on the
organometallic species during and after completion of the catalysis and on observations
made on stoichiometric reactions between the catalyst spcies and phenylacetylene, a new
proposal is made for a pathway to Z-selective linear dimerization of terminal alkynes by
rare earth metal catalysts. An important feature of this proposed pathway is that the C-C
bond formation takes place at coordinatively saturated metal species. This may provide an
explanation for the fact that essentially all rare earth metal catalysts that show selectivity
for Z-linear dimer formation are extremely selective indeed: the coordinative saturation
effectively shuts down migratory insertion pathways that produce the other isomers (linear
E-dimer and branched gem-dimer). It also helps to understand why rare earth metal
Cp-amido catalysts show their best performance in the presence of THF: the Lewis base
helps to break up dinuclear μ-alkynyl species which, in our proposed pathway, are not
involved in the actual catalytic cycle; breaking them up makes more of the metal species
available for catalysis and THF may be more effective for that than phenylacetylene.
Precedent for such a feature is found in the reactivity of a [(Cp-amine)V(-Cl)(PMe3)]2
complex, which does not react with alkynes unless it is first broken up by THF.18
Chapter 6
142
6.7 Experimental Section
General Remarks. See the corresponding section in Chapter 2. Phenylacetylene was
purchased from Merck and distilled from CaH2 after passing through a short neutral Al2O3
column prior to use. 2-Ethynylanisole and 4-Ethynylanisole were purchased from Aldrich
and distilled from CaH2 prior to use. 2-Ethynyl-1-methylpyrrole,15 2-ethynyltoluene,15
2-ethynylanisole,15 2-ethynylthiophene,15 3-ethynylthiophene,15 2-ethynylpyridine15, and
La(CH2Ph)3(THF)3,16
and La[N(SiMe3)2]317 were prepared according to literature
procedures.
Catalytic Dimerization of Phenylacetylenes by 26-35. Phenylacetylene (51.1 mg, 0.5
mmol) was added to a solution of complex 26-35 (10 μmol) in C6D6 (0.5 mL). The resulting
solution was transferred to an NMR tube equipped with a Teflon Young valve. The tube
was inserted into an NMR spectrometer which was preheated to 80 C and a single pulse
spectrum was taken every 5 min. The final volume of the reaction mixture is approximately
550 μL (500μL stock solution + ~50μL substrate) and [M] is ~18.2 mM.
Catalytic Dimerization of Phenylacetylenes by the Ionic Catalysts
(26-35)/[PhNMe2H][B(C6F5)4]. A solution of 26-35 (10 μmol) in C6D5Br (0.5 mL) was
added to [PhNMe2H][B(C6F5)4] (8.0 mg, 10 μmol) and then the resulting solution was
treated with phenylacetylene (51.1 mg, 0.5 mmol). The resulting mixture was transferred to
an NMR tube equipped with a Teflon Young valve. The tube was inserted into an NMR
spectrometer which was preheated to 80 C and a single pulse spectrum was taken every 5
min. The final volume of the reaction mixture is approximately 550 μL (500μL stock
solution + ~50μL substrate) and [M] is ~18.2 mM.
Catalytic Dimerization of (Hetero)aromatic Terminal Alkynes by the Ionic Catalyst
27/[PhNMe2H][B(C6F5)4]. A solution of 27 (5.2 mg, 10 μmol) in C6D5Br (0.5 mL) was
added to [PhNMe2H][B(C6F5)4] (8.0 mg, 10 μmol) and then the resulting solution was
treated with the (hetero)aromatic terminal alkynes a-h (0.5 mmol). The resulting mixture
was transferred to an NMR tube equipped with a Teflon Young valve. The tube was inserted
into an NMR spectrometer which was preheated to 80 C and a single pulse spectrum was
taken every 5 min. The final volume of the reaction mixture is approximately 550 μL
(500μL stock solution + ~50μL substrate) and [Y] is ~18.2 mM.
Catalytic Dimerization of (Hetero)aromatic Terminal Alkynes by the Neutral
Catalyst 28. A solution of complex 28 (5.6 mg, 10 μmol) in C6D6 (0.5 mL) was treated
with the (hetero)aromatic terminal alkynes a-f. The resulting solution was transferred to an
NMR tube equipped with a Teflon Young valve. The tube was inserted into an NMR
spectrometer which was preheated to 50 C or 80 C and a single pulse spectrum was taken
every 5 min. The final volume of the reaction mixture is approximately 550 μL (500μL
stock solution + ~50μL substrate) and [La] is ~18.2 mM.
Phenylacetylene Dimerization by the Ionic Catalyst 27/[PhNMe2H][B(C6F5)4] on a
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
143
Preparative Scale. C6H5Br (0.5 mL) was added to a mixture of (L6)Y(CH2Ph)2 (27, 2.6 mg,
5 μmol) and [PhMe2NH][B(C6F5)4] (4.0 mg, 5 μmol). The resulting mixture was
homogenized by agitation and phenylacetylene (1.02 g, 10 mmol) was added. The solution
was heated at 80 °C for 2.5 h and the NMR analysis indicated the full conversion. Hexane
(5 ml) was added to the reaction mixture and the resulting suspension was filtered. The
filtrate was dried under vacuum to give analytically pure Z-dimer of phenylacetylene (1.01
g, 9.9 mmol, 99%) as a yellow liquid. See below for analytical data of the enynes.
3-Ethynylthiophene Dimerization by the Ionic Catalyst 27/[PhNMe2H][B(C6F5)4] on
a Preparative Scale. C6H5Br (0.5 ml) was added to a mixture of (L6)Y(CH2Ph)2 (27, 2.6
mg, 5 μmol) and [PhMe2NH][B(C6F5)4] (4.0 mg, 5 μmol). The resulting mixture was
homogenized by agitation and 3-ethynylthiophene (0.54 g, 5 mmol) was added. The
solution was heated at 50 °C. The reaction was complete within 4 h as indicated by NMR
analysis. All the volatiles were removed under vacuum and the residue was purified by
crystallization from methanol to give the Z-dimer of 3-ethynylthiophene (0.51 g, 2.36 mmol,
94%) as a yellow crystalline solid.
Phenylacetylene Dimerization by the Neutral Catalyst 28 on a Preparative Scale. In
a single Schlenk tube, to a solution of compound (L6)La(CH2Ph)2 (28, 5.7 mg, 10 μmol) in
toluene (0.5 ml) was added phenylacetylene (1.02 g, 10 mmol) and the mixture was heated
for 1 h at 80˚C. All the volatiles were removed under reduced pressure and the residue was
passed through a short silica column with hexane as eluent to give the pure Z-dimer of
phenylacetylene (0.94 g, 9.2 mmol, 92%) as a pale yellow liquid after removal of the
volatiles.
Phenylacetylene Dimerization by [HL6 + La(CH2Ph)3(THF)3] on a Preparative Scale.
In a single Schlenk tube, a solution of HL6 (12.7 mg, 50 μmol) in toluene (0.5 mL) was
added to La(CH2Ph)3(THF)3 (41.4 mg, 50 μmol). To the resulting solution, phenylacetylene
(1.02 g, 10 mmol) was added and the mixture was heated for 1 h at 80˚C. All the volatiles
were removed under reduced pressure and the residue was passed through a short silica
column with hexane as eluent to give the pure Z-dimer of phenylacetylene (0.96 g, 9.4
mmol, 94%) as a pale yellow liquid after removal of the volatiles.
Characterization of Z-enynes. 1,1'-(1Z)-but-1-en-3-yne-1,4-diyldibenzene (Z-dimer
of alkyne a): 1H NMR (400 MHz, CDCl3), δ: 7.96 (d, 2H, JHH = 7.60 Hz), 7.52 (m, 2H),
7.41 (m, 2H), 7.36 (m, 4H), 6.73 (d, 1H, JHH = 11.9 Hz, PhCH=CH-C), 5.95 (d, 1H, JHH =
11.9 Hz, PhCH=CH-C). 13C NMR (100.6 MHz, CDCl3) δ: 138.6, 136.5, 131.4, 128.7, 128.5,
128.4, 128.3, 128.3, 123.4, 107.3, 95.8, 88.2. Anal. Calc for C16H12: C, 94.08%; H, 5.92%.
Found: 93.94%; H, 5.86%.
1,1'-(1Z)-but-1-en-3-yne-1,4-diylbis(2-methylbenzene) (Z-dimer of alkyne b): 1H NMR
(400 MHz, C6D5Br) δ: 8.14 (d, 1H, JHH = 7.58 Hz), 7.16 (d, 1H, JHH = 7.52 Hz), 6.89 (m,
2H), 6.80 (m, 2H), 6.76 (m, 2H), 6.50 (d, JHH = 11.8 Hz, CH=CH-C), 5.74 (d, JHH = 11.8
Chapter 6
144
Hz, CH=CH-C), 2.09 (s, 3H, CH3), 1.90 (s, 3H, CH3). 13C NMR (100.6 MHz, C6D5Br) δ:
139.8, 136.4, 136.1, 135.2, 132.0, 130.1, 129.5, 129.1, 128.3, 125.9, 125.54, 125.47, 123.2,
108.5, 94.2, 92.0, 20.8, 19.6. HR-MS: C18H16, cald.: 232.1252, found: 232.1257.
1,1'-(1Z)-but-1-en-3-yne-1,4-diylbis(2-methoxybenzene) (Z-dimer of alkyne c): 1H
NMR (500 MHz, C6D6) δ: 9.20 (d, 1H, JHH = 7.9 Hz), 7.45 (d, 1H, JHH = 7.6 Hz), 7.32 (d,
1H, JHH = 12.1 Hz), 7.12 (t, 1H, JHH = 7.7 Hz), 7.0 (t, 1H, JHH = 7.5 Hz), 6.97 (t, 1H, JHH =
7.8 Hz), 6.68 (t, 1H, JHH = 7.5 Hz), 6.52 (d, 1H, JHH = 8.2 Hz), 6.41 (d, 1H, JHH = 8.2 Hz),
6.00 (d, 1H, JHH = 12.1 Hz), 3.32 (s, 3H), 3.26 (s, 3H). {1H}13C NMR (500 MHz, C6D6) δ:
160.8, 157.4, 133.5, 132.5, 129.8, 129.6, 129.4, 126.2, 120.6, 120.5, 113.7, 110.9, 110.6,
107.5, 93.4, 55.2, 55.0. One carbon signal is overlaped. HR-MS: C18H16O2, cal.: 264.1150,
found: 264.1137.
1,1'-(1Z)-but-1-en-3-yne-1,4-diylbis(4-methoxybenzene) (Z-dimer of alkyne d): 1H
NMR (500 MHz, C6D6) δ: 7.97 (d, 1H, JHH = 8.6 H), 7.42 (d, 1H, JHH = 8.7 Hz), 6.79 (d,
1H, JHH = 8.7 Hz), 6.60 (d, 1H, JHH = 8.7 Hz), 6.44 (d, 1H, JHH = 11.8 Hz, PhCH=CH), 5.81
(d, 1H, JHH = 11.8 Hz, PhCH=CH), 3.27 (s, 3H, CH3OPh), 3.18 (s, 3H, CH3OPh). {1H}13C
NMR (500 MHz, C6D6, δ): 160.2, 160.1, 138.0, 133.2, 130.7, 130.3, 116.3, 114.5, 114.0,
105.5, 96.2, 88.2, 54.7(5), 54.7(3).
2,2'-(1Z)-but-1-en-3-yne-1,4-diyldithiophene (Z-dimer of alkyne e): 1H NMR (400
MHz, C6D6) δ: 7.63 (d, 1H, JHH = 5.1 Hz), 7.55 (d, 1H, JHH = 2.9 Hz), 7.09 (d, 1H, JHH
=3.0), 6.94 (d, 1H, JHH = 5.0 Hz), 6.87 (dd, 1H, JHH = 5.1 Hz, JHH = 3.0 Hz), 6.70 (dd, 1H,
JHH = 5.0 Hz, JHH = 2.9 Hz), 6.39 (d, 1H, JHH = 11.8 Hz), 5.65 (d, 1H, JHH = 11.8 Hz).
{1H}13C NMR (500 MHz, C6D6) δ: 139.2, 132.8, 129.7, 128.7, 128.1, 125.9, 125.7, 125.4,
122.9, 106.2, 91.7, 88.7.
3,3'-(1Z)-but-1-en-3-yne-1,4-diyldithiophene (Z-dimer of alkyne f): 1H NMR (400
MHz, CDCl3) δ: 7.79 (d, 1H, JHH = 3.0 Hz), 7.68 (d, 1H, JHH = 5.0 Hz), 7.49 (d, 1H, JHH =
3.0 Hz), 7.30 (m, 2H), 7.17 (m, 1H), 6.71 (d, JHH = 11.7 Hz, CH=CH-C), 5.78 (d, JHH =
11.7 Hz, CH=CH-C). 1H NMR (100.6 MHz, CDCl3) δ: 138.6, 132.4, 129.5, 128.5, 127.7,
125.5, 125.4, 125.1, 122.3, 105.8, 91.1, 88.1. HR-MS: C12H8S2, cald.: 216.0067, found:
216.0054. Anal. Calc for C12H8S2: C, 66.63%; H, 3.73%. Found: C, 66.62%; H, 3.77%.
3,3'-(1Z)-but-1-en-3-yne-1,4-diylbis(1-methyl-1H-pyrrole) (Z-dimer of alkyne g): 1H
NMR (400 MHz, CDCl3) δ: 7.32 (dd, 1H, JHH = 3.8 Hz, JHH = 1.7 Hz), 6.71 (dd, 1H, JHH =
2.6 Hz, JHH = 1.7 Hz), 6.68 (dd, 1H, JHH = 2.6 Hz, JHH = 1.7 Hz), 6.56 (d, 1H, JHH = 12.4
Hz, CH=CH-C), 6.54 (dd, 1H, JHH = 3.8 Hz, JHH = 1.7 Hz), 6.23 (dd, 1H, JHH = 3.8 Hz, JHH
= 2.6 Hz), 6.17 (dd, 1H, JHH = 3.8 Hz, JHH = 2.6 Hz), 5.71 (d, 1H, JHH = 12.4 Hz,
CH=CH-C), 3.76 (s, 3H, NCH3), 3.66 (s, 3H, NCH3). 13C NMR (100.6 MHz, CDCl3) δ:
130.6, 128.4, 124.4, 123.7, 116.1, 115.0, 110.9, 108.23, 108.17, 101.6, 92.8, 88.2, 34.6,
33.6. HR-MS: C14H14N2, cal.: 210.1157, found: 210.1147.
Synthesis of (L6)Sc(C≡CPh)2 (40). To a solution of (L6)Sc(CH2Ph)2 (26, 144.2 mg, 0.3
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
145
mmol) in toluene (35 mL), a solution of phenylacetylene (61.3 mg, 0.6 mmol) in toluene (2
mL) was added. The resulting solution was stirred overnight at room temperature and then
all the volatiles were removed under vacuum. The residue was dissolved in benzene (2 mL)
and hexane (1 mL) was added, followed by filtration. Upon standing at room temperature
overnight, crystalline material formed (including material suitable for single-crystal X-ray
analysis). The mother liquor was decanted and the solid was dried under reduced pressure,
yielding the titled compound as a white solid (110.2 mg, 0.22 mmol, 73%). 1H NMR
(400MHz, C6D6, 25 C) δ: 7.65 (d, 4H, JCH = 7.68 Hz, o-H Ph), 7.07 (t, 4H, JCH = 7.91 Hz,
m-H Ph), 6.97 (t, 2H, JCH = 7.23 Hz, p-H Ph), 3.78 (m, 2H, α-H Py), 3.28 (m, 2H, NCH2),
3.03 (m, 2H, NCH2-bridge), 2.79 (m, 2H, NCH2-bridge), 2.62 (d, 2H, JHH = 11.6 Hz,
CCH2N), 2.58 (s, 6H, NCH3), 2.32 (m, 2H, α-H Py), 2.17 (m, 2H, β-H Py), 1.91 (d, 2H, JHH
= 11.6 Hz, CCH2N), 1.83 (m, 2H, NCH2), 1.47 (m, 2H, β-H Py), 0.64 (s, 3H, CCH3). 13C
NMR (100.5 MHz, C6D6, 25 °C) δ: 142.1 (br, ScC≡C-Ph), 132.0 (dt, JCH = 159.5 Hz, JCH =
6.6 Hz, o-C Ph), 128.2 (dd, JCH = 158.9 Hz, JCH = 7.7 Hz, m-C Ph), 125.7 (dt, JCH = 160.1
Hz, JCH = 7.7 Hz, p-C Ph), 102.6 (t, JCH = 4.6 Hz, ScC≡CPh), 74.7 (t, JCH = 133.2 Hz,
CCH2), 59.6 (t, JCH = 135.6 Hz, Azepine-NCH2-bridge), 57.8 (s, CCH3), 57.4 (t, JCH =
137.5 Hz, NCH2CH2-Azepine), 54.4 (t, JCH = 139.3 Hz, α-C Py), 51.4 (q, JCH = 135.6 Hz,
NCH3), 45.8 (t, JCH = 128.4 Hz, Py-CH2-bridge), 23.1 (t, JCH = 133.0 Hz, β-C Py), 19.5 (q,
JCH = 124.8 Hz, CCH3). Anal. Calc for C28H43N4Sc: C, 71.98; H, 7.85; N, 11.19. Found: C:
71.88; H, 7.89; N, 11.09.
Synthesis of [(L6)Y(C≡CPh)(μ-C≡CPh)]2 (41). A solution of (L6)Y(CH2Ph)2 (27, 104.9
mg, 0.2 mmol) in toluene (1 mL) was added to phenylacetylene (40.9 mg, 0.4 mmol) and
the resulting mixture was kept for 30 min at room temperature and then at -30 °C overnight,
after which crystalline material had formed (including the material for single-crystal X-ray
analysis). The mother liquor was decanted and the solid was dried under vacuum to giving
the title compound (76.2 mg, 0.07 mmol, 70%) as a colorless solid. 1H NMR (500MHz,
C6D6, 25°C) δ: 7.76 (br, 8H, o-H Ph), 7.07 (t, 8H, JHH = 7.24 Hz, m-H Ph), 6.95 (t, 4H, JHH
= 6.44 Hz, p-H Ph), 3.54 (m, 4H, NCH2), 3.39 (br, 8H, α-H Py), 3.13 (m, 4H, NCH2-bridge),
3.05 (m, 4H, NCH2-bridge), 2.83 (s, 12H, NCH3), 2.70 (d, 4H, JHH = 11.0 Hz, CCH2N),
1.99 (d, 4H, JHH = 11.0 Hz, CCH2N), 1.98 (m, 4H, NCH2), 1.80 (br, 8H, β-H Py), 0.75 (s,
6H, CCH3). 13C NMR (125.7 MHz, C7D8, 25°C) δ: 148.4 (s, C≡CPh), 132.1 (d, JCH = 161.6
Hz, o-C Ph), 128.3 (d, JCH = 158.9 Hz, m-C Ph), 126.3 (d, JCH = 160.2 Hz, p-C Ph), 114.9
(br, C≡CPh), 77.6 (t, JCH = 135.7 Hz, CCH2N), 58.6 (t, JCH = 135.5 Hz,
NCH2CH2-Azepine), 58.3 (t, JCH = 133.3 Hz, Azepine-NCH2-bridge), 57.7 (s, CCH3), 54.4
(t, JCH = 137.8 Hz, α-C Py), 52.6 (q, JCH = 135.5 Hz, NCH3), 47.1 (t, JCH = 128.9 Hz,
Py-CH2-bridge), 23.5 (t, JCH = 131.2 Hz, β-C Py), 19.8 (q, JCH = 125.4 Hz, CCH3). The
ipso-C resonance is obscured by the solvent peaks. Anal. Calc for C60H78Y2N8: C, 66.17; H,
7.22; N, 10.29. Found: C: 66.16; H, 7.37; N, 9.89.
Characterization of (L6)Y(C≡CPh)2(THF-d8)x. Once dissolved in THF-d8, the
Chapter 6
146
binuclear yttrium dialkynyl complex was cleaved into mononuclear species
(L6)Y(C≡CPh)2(THF-d8)x, as seen by NMR spectroscopy. 1H NMR (500 MHz, THF-d8, -20
˚C) δ: 7.19 (d, JHH = 7.2 Hz, 4 H, o-H-Ph), 7.12 (t, 4H, JHH = 7.6 Hz, m-H-Ph), 7.02 (t, 2H,
JHH = 7.2 Hz, p-H-Ph), 4.04 (m, 2H, α-H Py), 3.17 (m, 4H, NCH2-bridge), 3.14 (m, 2H,
NCH2), 2.82 (d, JHH = 11.2 Hz, 2H, CCH2), 2.70 (s, 6H, NCH3), 2.61 (m, 2H, α-H Py), 2.50
(m, 2H, NCH2), 2.42 (d, 2H, JHH = 11.2 Hz, CCH2N, 2.23 (m, 2H, β-H Py), 1.73 (m, 2H,
β-H Py), 0.83 (s, 3H, CCH3). 13C NMR (125.7 MHz, THF-d8, -20 ˚C) δ: 149.2 (d, JYC =
52.9 Hz, YC≡CPh), 132.9 (dt, JCH = 159.4Hz, JCH = 6.7 Hz, o-C-Ph), 130.7 (t, JCH = 8.0 Hz,
ipso-C-Ph), 129.7 (dd, JCH = 158.5 Hz, JCH = 7.7 Hz, m-C-Ph), 126.6 (dt, JCH = 160.2 Hz,
JCH = 7.9 Hz, p-C-Ph), 105.7 (d, JYC = 9.9 Hz, YC≡CPh), 79.6 (t, JCH = 132.6 Hz, CCH2),
61.5 (t, JCH = 132.0 Hz, NCH2-bridge), 60.2 (t, JCH = 134.1 Hz, NCH2), 58.8 (s, CCH3),
56.5 (t, JCH = 138.3 Hz, α-C Py), 53.9 (q, JCH = 135.9 Hz, NCH3), 48.5 (t, JCH = 128.3 Hz,
NCH2-bridge), 25.8 (t, JCH = 131.4 Hz, β-C Py), 21.3 (q, JCH = 124.6 Hz, CCH3).
Synthesis of [(L6)La(C≡CPh)(μ-C≡CPh)]2 (42). To a solution of (L6)La(CH2Ph)2 (28,
116.4 mg, 0.2 mmol) in toluene (2 mL), was added phenylacetylene (40.9 mg, 0.4 mmol).
The resulting mixture was left standing at -30 °C overnight, after which crystalline material
had formed. The mother liquor was decanted and the solid was dried under vacuum
yielding the title compound as a colorless solid (72.8 mg, 65.8 μmol, 66%). Crystals
suitable for single-crystal X-ray analysis were grown by crystallization from THF/hexane. 1H NMR (500MHz, C7D8, 25°C) δ: 7.81 (d, 8H, JHH = 7.53 Hz, o-H Ph), 7.12 (t, 8H, JHH =
7.76 Hz, m-H Ph), 6.98 (t, 4H, JHH = 7.42 Hz, p-H Ph), 4.12 (br, 4H, α-H Py), 3.55 (m, 4H,
NCH2), 3.16 (m, 4H, NCH2-bridge), 3.08 (m, 4H, NCH2-bridge), 2.83 (s, 12H, NCH3), 2.72
(d, 4H, JHH = 11.6 Hz, CCH2N), 2.48 (br, 4H, α-H Py), 2.46 (br, 4H, β-H Py), 2.06 (m, 4H,
NCH2), 2.05 (d, 4H, JHH = 11.6 Hz, CCH2N), 1.72 (br, 4H, β-H Py), 0.73 (s, 6H, CCH3). 13C NMR (125.7 MHz, C7D8, 25°C) δ: 162.1 (s, LaC≡CPh), 132.2 (d, JCH = 161.3 Hz, o-C
Ph), 128.3 (d, JCH = 167.4 Hz, m-C Ph), 126.2 (d, JCH = 162.9 Hz, p-C Ph), 115.5 (br,
C≡CPh), 76.9 (t, JCH = 132.3 Hz, CCH2N), 60.1 (t, JCH = 133.9 Hz, Azepine-NCH2-bridge),
58.4 (t, JCH = 136.0 Hz, NCH2CH2-Azepine), 54.6 (t, JCH = 138.1 Hz, α-C Py), 54.4 (s,
CCH3), 51.5 (q, JCH = 136.0 Hz, NCH3), 48.0 (t, JCH = 127.7 Hz, Py-CH2-bridge), 24.3 (t,
JCH = 131.4 Hz, β-C Py), 19.8 (q, JCH = 126.2 Hz, CCH3). The ipso-C resonance is obscured
by the solvent peaks. Assignment of NMR resonances was aided by COSY and HSQC
experiments. Anal. Calc for C60H78La2N8: C, 60.60; H, 6.61; N, 9.42. Found: C: 59.25; H,
6.59; N, 9.30. The rather low carbon content found (whereas H and N values agree with the
calculated values) is likely to be due to some carbide formation. We have observed this
before on a La-acetylide compound.4a
Synthesis of (HL6)Sc(C≡CPh)3 (43). A solution of (L6)Sc(CH2Ph)2 (26, 210.0 mg, 0.45
mmol) in C6H6 (2 mL) was added to phenylacetylene (143.0 mg, 1.40 mmol) and the
mixture was stirred for 30 min at room temperature. n-Hexane (4 mL) was carefully layered
on top of the resulting solution. Upon standing overnight at room temperature, crystalline
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
147
material formed (including crystals suitable for X-ray analysis). The mother liquor was
decanted and the solid was dried under reduced pressure, yielding 43+0.5(C6H14) (208.9 mg,
0.35 mmol, 77%) as a colorless solid. The (1H and 13C) NMR spectra of this complex
indicated the decomposition to the dialkynyl complex 40 with liberation of 1 equiv of free
phenyacetylene.
Synthesis of (HL6)Y(C≡CPh)3 (44). To a solution of (L6)Y(CH2SiMe3)2 (32, 258.4 mg,
0.50 mmol) in toluene (2 mL) was added a solution of phenylacetylene (178.7 mg, 1.75
mmol) in toluene (1 mL) and the resulting mixture was allowed to stand at room
temperature for 20 min. Upon cooling to -30 ºC overnight, crystalline material formed. The
mother liquor was decanted and the solid was dried under vacuum, yielding the title
compound (269.7 mg, 0.42 mmol, 83%) as an off-white powder. The crystals suitable for
sing-crystal X-ray analysis were grown from a toluene/THF solution at -30 ºC. 1H NMR
(500 MHz, THF-d8, 23 ºC) δ: 7.23 (d, 6H, JHH = 7.6 Hz, o-H Ph), 7.11 (t, 6H, JHH = 7.6 Hz,
m-H Ph), 7.02 (t, 3H, JHH = 7.3 Hz, p-H Ph), 4.16 (m, 1H, NCH2), 3.84 (m, 1H, NCH2),
3.75 (m, 1H, CH2-bridge), 3.74 (s, 1H, NH), 3.40 (m, 1H, CH2-bridge), 3.21 (d, 1H, JHH =
13.4 Hz, CCH2), 3.09 (d, 1H, JHH = 14.2 Hz, CCH2), 2.95 (s, 3H, NCH3), 2.91 (s, 3H,
NCH3), 2.77 (m, 1H, CH2-bridge), 2.67 (m, 2H, α-H Py), 2.61 (m, 2H, α-H Py), 2.56 (m,
1H, CH2-bridge), 2.55 (d, 1H, JHH = 13.4 Hz, CCH2), 2.49 (m, 1H, NCH2), 2.44 (m, 1H,
NCH2), 2.43 (d, 1H, JHH = 14.2 Hz, CCH2), 1.61 (m, 4H, β-H Py), 1.07 (s, 3H, CCH3).
{1H}13C NMR (125.7 MHz, THF-d8, -50 ºC) δ:150.0 (d, JYC = 51.4 Hz, YC≡CPh), 148.6 (d,
JYC = 47.7 Hz, YC≡CPh), 147.8 (d, JYC = 50.6 Hz, YC≡CPh), 133.1 (o-C Ph), 132.9 (o-C
Ph), 130.4 (ipso-C Ph), 130.3 (ipso-C Ph), 130.2 (ipso-C Ph), 129.78 (m-C Ph), 129.74
(m-C Ph), 129.70 (m-C Ph), 126.9 (p-C Ph), 126.8 (p-C Ph), 105.8 (d, JYC = 9.4 Hz,
YC≡CPh), 103.5 (d, JYC = 10.0 Hz, YC≡CPh), 102.2 (d, JYC = 10.2 Hz, YC≡CPh), 75.9
(CCH2), 67.4 (CCH2), 62.4 (NCH2), 61.6 (NCH2), 58.8 (CCH3), 57.3 (CH2-bridge), 56.2
(α-C Py), 53.6 (NCH3), 52.1 (NCH3), 43.4 (CH2-bridge), 25.4, (β-C Py), 21.7 (CCH3).
In situ Generation of of (HL6)La(C≡CPh)3 (45) on an NMR-tube scale. A solution of
(L6)La(CH2Ph)2 (28, 16.8 mg, 30 μmol) in THF-d8 (0.5 mL) was added to phenylacetylene
(9.3 mg, 91 μmol). The resulting solution was transferred to an NMR tube equipped with a
Teflon Young valve and analyzed by NMR spectroscopy, which indicated a clean formation
of the title complex and 2 equiv of toluene. 1H NMR (500 MHz, THF-d8, 23 ºC) δ: 7.19 (d,
6H, JHH = 7.6 Hz, o-H Ph), 7.06 (t, 6H, JHH = 7.6 Hz, m-H Ph), 6.96 (t, 3H, JHH = 7.4 Hz,
p-H Ph), 4.10 (m, 1H, NCH2), 3.83 (m, 1H, NCH2), 3.80 (m, 1H, NH), 3.35 (m, 2H, α-H
Py), 3.29 (m, 1H, CH2-bridge), 3.13 (d, 1H, JHH = 13.0 Hz, CCH2), 3.11 (s, 3H, NCH3),
3.02 (m, 2H, α-H Py), 2.97 (m, 1H, CH2-bridge), 2.95 (s, 3H, NCH3), 2.92 (d, 1H, JHH =
13.9 Hz, CCH2), 2.78 (m, 1H, CH2-bridge), 2.75 (m, 1H, CH2-bridge), 2.58 (d, 1H, JHH =
13.9 Hz, CCH2), 2.57 (m, 1H, NCH2), 2.46 (d, 1H, JHH = 14.2 Hz, CCH2), 2.38 (m, 1H,
NCH2), 2.06 (m, 2H, β-H Py), 2.02 (m, 2H, β-H Py), 1.06 (s, 3H, CCH3). {1H}13C NMR
(125.7 MHz, THF-d8, -50 ºC) δ: 132.7 (o-C Ph), 129.2 (m-C Ph), 125.9 (p-C Ph), 77.5
Chapter 6
148
(CCH2), 64.5 (CCH2), 61.2 (NCH2), 60.2 (CH2-bridge), 57.8 (α-C Py), 57.7 (NCH2), 53.5
(NCH3), 51.8 (NCH3), 42.6 (CH2-bridge), 25.3 (β-C Py), 21.4 (CCH3).
In situ Generation of [(L6)Y(CH2Ph)(THF-d8)x][B(C6F5)4] on an NMR-tube scale. A
solution of (L6)Y(CH2Ph)2 (27, 43.1 mg, 82.2 μmol) in THF-d8 (0.6 ml) was added to
[PhMe2NH][B(C6F5)4] (65.8 mg, 82.2 μmol) at room temperature. The resulting suspension
was homogenized by agitation and the solution was transferred to an NMR tube equipped
with a Teflon Young valve. It was then analyzed by NMR spectroscopy, which indicated a
clean conversion to the cationic species, toluene, and free PhNMe2. 1H NMR (500 MHz,
THF-d8) δ: 7.10 (t, 2H, JHH = 7.60 Hz, m-H Ph), 6.57 (t, 1H, JHH = 7.28 Hz, p-H PhCH2),
6.44 (d, 2H, JHH = 7.70 Hz, o-H PhCH2), 2.96 (m, 4H, α-H Py), 2.93 (t, 2H, JHH = 5.10 Hz,
NCH2-bridge), 2.91 (d, 2H, JHH = 12.3 Hz, CCH2N), 2.83 (t, 2H, JHH = 5.10 Hz,
NCH2-bridge), 2.47 (d, 2H, JHH = 12.3 Hz, CCH2N), 2.29 (s, 6H, NCH3), 2.25 (br, 4H,
NCH2), 1.86 (m, 4H, β-H Py), 1.51 (s, 2H, YCH2), 0.74 (s, 3H, CCH3). 13C NMR (125.7
MHz, THF-d8) δ: 150.3 (d, JCF = 242.1 Hz, o-C C6F5), 154.5 (s, ipso-C Ph), 140.3 (d, JCF =
236.3 Hz, p-C C6F5), 138.4 (d, JCF = 245.4 Hz, m-C C6F5), 134.0 (t, JCH = 156.1 Hz, m-C
Ph), 126.3 (b, ipso-C-C6F5), 121.5 (d, JCH = 151.6 Hz, o-C Ph), 119.7 (d, JCH = 161.2 Hz,
p-C Ph), 77.8 (t, JCH = 132.6 Hz, CCH2N), 61.7 (t, JCH = 136.4 Hz, NCH2-bridge), 58.8 (s,
CCH3), 58.8 (t, JCH = 137.0 Hz, α-C Py), 55.0 (t, JCH = 132.8 Hz, NCH2), 53.0 (dt, JYC =
21.4 Hz, JCH = 129.5 Hz, YCH2), 50.4 (q, JCH = 137.3 Hz, NCH3), 47.5 (t, JCH = 128.0 Hz,
NCH2-bridge), 24.7 (t, JCH = 134.1 Hz, β-C Py), 21.6 (q, JCH = 126.6 Hz, CCH3).
In situ Generation of [(L6)Y(THF-d8)x][B(C6F5)4]2 on an NMR-tube scale. A solution
of (L6)Y(CH2Ph)2 (27, 11.6 mg, 22.1 μmol) in THF (0.4 ml) was added to
[PhNMe2H][B(C6F5)4] (35.4 mg, 44.2 mmol) and the mixture was homogenized by
agitation. The resulting solution was transferred to an NMR tube equipped with a Teflon
(Young) valve and analyzed by NMR spectroscopy, which indicated a clean conversion to
the corresponding dicationic species, 2 equiv of toluene, and free PhNMe2. 1H NMR (500
MHz, THF-d8, 25 ˚C) δ 3.22 (m, 2H, NCH2), 3.19 (d, 2H, JHH = 12.5 Hz, CCH2), 3.11 (t,
2H, JHH = 5.5 Hz, NCH2-bridge), 2.94 (m, 2H, NCH2), 2.93 (m, 4H, Py α-H), 2.92 (t, 2H,
JHH = 5.6 Hz, NCH2-bridge), 2.84 (d, 2H, JHH = 12.3 Hz, CCH2), 2.64 (s, 6H, NCH3), 1.98
(m, 4H, Py β-H), 0.89 (s, 3H, CCH3). 13C NMR (125.7 MHz, THF-d8, 25 ˚C) δ 150.3 (d,
JCF = 242.1 Hz, o-C C6F5), 140.3 (d, JCF = 236.3 Hz, p-C C6F5), 138.4 (d, JCF = 245.4 Hz,
m-C C6F5), 126.3 (b, ipso-C-C6F5), 80.3 (t, JCH = 138.5 Hz, CCH2), 60.0 (t, JCH = 138.2 Hz,
NCH2), 59.2 (d, JYC = 3.4 Hz, CCH3), 58.3 (t, JCH = 131.8 Hz, NCH2-bridge), 54.4 (t, JCH =
138.4 Hz, Py α-C), 51.5 (q, JCH = 136.2 Hz, NCH3), 47.2 (t, JCH = 131.3 Hz, NCH2-bridge),
23.9 (t, JCH = 135.6 Hz, Py β-C), 20.5 (q, JCH = 127.3 Hz, CCH3).
In situ Generation of [(L6)Y(C≡CPh)(THF-d8)x][B(C6F5)4]. Method A: A solution of
in situ generated monocationic species [(L6)Y(CH2Ph)(THF-d8)x][B(C6F5)4] (82.2 μmol) in
THF-d8 (0.6 mL) was added to phenylacetylene (8.4 mg, 82.2 μmol) and the resulting
solution was transferred to an NMR tube equipped with a Teflon Young valve and analyzed
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
149
by NMR spectroscopy, which indicated a clean conversion to the title cationic monoalkynyl
species and toluene. Method B: A solution of in situ generated dicationic species
[(L6)Y(THF-d8)x][B(C6F5)4]2 (22.1 μmol) was added to [(L6)Y(C≡CPh)(μ-C≡CPh)]2 (41,
12.0 mg, 22.1 μmol) and the resulting solution was transferred to an NMR tube equipped
with a Teflon (Young) valve and analyzed by NMR spectroscopy, which indicated a clean
conversion to the cationic species [(L6)Y(C≡CPh)(THF-d8)x][B(C6F5)4]. 1H NMR (500
MHz, THF-d8) δ: 7.16 (t, 2H, JHH = 7.8 Hz, m-H Ph), 7.12-7.05 (m, 3H, o-H and p-H Ph),
3.34 (br, 4H, Py α-H), 3.27 (m, 2H, NCH2), 3.09(t, 2H, JHH = 5.4 Hz, NCH2-bridge), 3.00
(d, 2H, JHH = 11.9 Hz, CCH2), 2.83 (t, 2H, JHH = 5.4 Hz, NCH2-bridge), 2.70 (m, 2H,
NCH2), 2.65 (d, 2H, JHH = 11.9 Hz, CCH2), 2.65 (s, 6H, NCH3), 1.92 (m, 4H, Py β-H), 0.86
(s, 3H, CCH3). 13C NMR (125.7 MHz, THF-d8) δ: 150.3 (d, JCF = 242.1 Hz, o-C C6F5),
145.5 (d, JYC = 53.2 Hz, YC≡CPh), 140.3 (d, JCF = 236.3 Hz, p-C C6F5), 138.4 (d, JCF =
245.4 Hz, m-C C6F5), 132.9 (dt, JCH = 160.0 Hz, JCH = 6.4 Hz, m-C Ph), 129.9 (dd, JCH =
159.3 JCH = 7.3 Hz, o-C Ph), 129.1 (t, JCH = 7.7 Hz, ipso-C Ph), 127.8 (dt, JCH = 160.7 Hz,
JCH = 7.3 Hz, p-C Ph), 126.3 (b, ipso-C C6F5), 106.8 (d, JYC = 9.8 Hz, YC≡CPh), 79.1 (t,
JCH = Hz, CCH2), 60.0 (t, JCH = 134.4 Hz, NCH2-bridge), 59.4 (t, JCH = 136.6 Hz, NCH2),
59.3 (d, JYC = 2.7 Hz, CCH3), 54.9 (t, JCH = 140.0 Hz, Py α-C), 52.0 (q, JCH = 136.1 Hz,
NCH3), 48.2 (dt, JYC =2.3 Hz, JCH = 129.4 Hz, NCH2-bridge), 24.5 (t, JCH = 133.1 Hz, Py
β-C), 21.2 (q, JCH = 125.8 Hz, CCH3).
Reaction of [(L6)Y(C≡CPh)(μ-C≡CPh)]2 with [PhNMe2H][B(C6F5)4] on an NMR
scale. THF-d8 (0.6 mL) was added to a mixture of [(L6)Y(C≡CPh)(μ-C≡CPh)]2 (41, 52.7
mg, 24.2 μmol) and [PhNMe2H][B(C6F5)4] (77.5 mg, 48.4 μmol) and the mixture was
homogenized by agitation. The resulting solution was transferred to an NMR tube equipped
with a Teflon (Young) valve and analyzed by NMR spectrometry, which indicated the clean
formation of [(HL6)Y(C≡CPh)2(THF-d8)x][B(C6F5)4]. 1H NMR (500 MHz, THF-d8, -20 ˚C,
δ): 7.30-7.10 (12 H, YC≡CPh), 4.20 (m, 1H, Py α-H), 3.94 (dd, JHH = 11.8 Hz, JHH = 4.3 Hz,
1H, NH), 3.68 (m, 1H, Py α-H), 3.53 (m, 1H, NCH2), 3.50 (m, 1H, Py α-H), 3.31 (m, 1H,
NCH2), 3.29 (m, 1H, NCH2-bridge), 3.21 (d, 1H, JHH = 14.6 Hz, CCH2N), 3.06 (m, 1H, Py
α-H), 3.05 (d, 1H, JHH = 12.6 Hz, CCH2N), 3.00 (m, 2H, NCH2-bridge), 2.99 (s, 3H, NCH3),
2.96 (m, 1H, NCH2-bridge), 2.92 (m, 1H, NCH2), 2.85 (d, 1H, JHH = 14.6 Hz, CCH2N),
2.77 (m, 1H, NCH2), 2.75 (s, 3H, NCH3), 2.73 (d, 1H, JHH = 12.6 Hz, CCH2N), 2.01 (m, 4H,
β-H Py), 1.11 (s, 3H, CCH3). 13C NMR (125.7 MHz, THF-d8, -20 ˚C, δ): 150.3 (d, JCF =
242.1 Hz, o-C-C6F5), 144.9 (d, JYC = 51.3 Hz, YC≡CPh), 144.2 (d, JYC = 53.0 Hz,
YC≡CPh), 140.3 (d, JCF = 236.3 Hz, m-C C6F5), 138.4 (d, JCF = 245.4 Hz, m-C C6F5), 133.1
(dt, JCH = 160.3, JCH = 6.6 Hz, m-C Ph), 130.1 (dd, JCH = 159.5 Hz, JCH = 6.5 Hz, o-C Ph),
130.0 (dd, JCH = 159.5 Hz, JCH = 6.5 Hz, o-C Ph), 128.2 (t, JCH = 8.0 Hz, Cipso Ph), 128.2 (dt,
JCH = 161.5 Hz, JCH = 7.5 Hz, p-C Ph), 128.1 (dt, JCH = 161.1 Hz, JCH = 7.5 Hz, p-C Ph),
126.3 (br, Cipso C6F5), 107.0 (d, JYC = 10.4 Hz, YC≡CPh), 105.1 (d, JYC = 9.2 Hz, YC≡CPh),
77.3 (t, JCH = 137.8 Hz, CCH2N), 63.0 (t, JCH = 135.0 Hz, CCH2N), 59.6 (t, JCH = 137.4 Hz,
NCH2-bridge), 59.4 (s, CCH3), 59.2 (t, JCH = 140.4 Hz, Py α-C), 58.5 (t, JCH = 137.5 Hz,
Chapter 6
150
NCH2), 56.6 (t, JCH = 133.2 Hz, NCH2), 55.5 (t, JCH = 137.5 Hz, Py α-C), 51.8 (q, JCH =
137.7 Hz, NCH3), 51.5 (q, JCH = 137.7 Hz, NCH3), 42.8 (t, JCH = 135.4 Hz, NCH2-bridge),
24.8 (t, JCH = 133.3 Hz, Py β-C), 24.5 (t, JCH = 133.3 Hz, Py β-C), 19.8 (q, JCH = 127.7 Hz,
CCH3).
Synthesis of [(HL6)Y(C≡CPh)2(THF)][B(C6H5)4] (46). To a mixture of (L6)Y(CH2Ph)2
(27, 183.6 mg, 0.35 mmol) and [PhNMe2H][B(C6H5)4] (154.5 mg, 0.35 mmol) was added a
solution of phenylacetylene (71.5 mg, 0.70 mmol) in THF (1 mL) and the resulting solution
was stirred for 30 min at room temperature. All the volatiles were removed under reduced
pressure and the residue was purified by recrystallization from a THF/toluene solution at
-30 º, yielding the title compound (267.1mg, 0.29 mmol, 81%) as a colorless crystalline
solid (including crystals suitable for X-ray analysis). The NMR spectroscopy of the cation
in 46 is identical to that of in situ generated [(HL6)Y(C≡CPh)2(THF-d8)x]+. Anal. Calc for
C58H68BN4OY: C, 74.35; H, 7.32; N, 5.98. Found: C: 74.32; H, 7.35; N, 5.84.
In situ Generation of [(L6)La(CH2Ph)(THF-d8)x][B(C6F5)4] on an NMR-tube scale.
THF-d8 (0.6 mL) was added to a mixture of (L6)La(CH2Ph)2 (28, 42.9 mg, 74.7 μmol) and
[PhMe2NH][B(C6F5)4] (59.8 mg, 74.7 μmol) and the suspension was homogenized by
agitation. The resulting solution was transferred to an NMR tube equipped with a Teflon
Young valve and was analyzed by NMR spectroscopy, which indicated a clean formation of
the corresponding cationic species, one equiv of toluene, and PhNMe2. 1H NMR (500 MHz,
THF-d8) δ: 7.04 (t, 2H, JHH =7.6 Hz, m-H Ph), 6.43 (t, 1H, JHH = 7.1 Hz, p-H Ph), 6.32 (d,
2H, JHH = 7.4 Hz, o-H Ph), 3.07 (m, 2H, NCH2), 3.04 (t, 2H, JHH = 5.4 Hz, NCH2-bridge),
2.95 (d, 2H, JHH = 12.3 Hz, CCH2), 2.74 (t, 2H, JHH = 5.4 Hz, NCH2-bridge), 2.68 (m, 2H,
NCH2), 2.63 (d, 2H, JHH = 12.3 Hz, CCH2), 2.52 (s, 6H, NCH3), 2.51 (m, 4H, α-H Py), 1.78
(m, 4H, β-H Py), 1.64 (s, 2H, LaCH2), 0.80 (s, 3H, CCH3). 13C NMR (125.7 MHz, THF-d8)
δ: 154.1 (s, ipso-C Ph), 150.3 (d, JCF = 242.1 Hz, o-C C6F5), 140.3 (d, JCF = 236.3 Hz, p-C
C6F5), 138.4 (d, JCF = 245.4 Hz, m-C C6F5), 132.8 (t, JCH = 154.7 Hz, JCH = 7.4 Hz, m-C Ph),
126.3 (b, ipso-C-C6F5), 122.0 (dt, JCH = 151.3 Hz, JCH = 6.7 Hz, o-C Ph), 117.8 (dt, JCH =
160.7 Hz, JCH = 7.2 Hz, p-C-PhCH2), 77.1 (t, JCH = 134.1 Hz, CCH2N), 67.4 (t, JCH = 130.0
Hz, LaCH2), 61.6 (s, CCH3), 59.5 (t, JCH = 133.5 Hz, NCH2-bridge), 59.0 (t, JCH = 136.8 Hz,
NCH2), 52.7 (t, JCH = 138.6 Hz, α-C Py), 51.1 (q, JCH = 136.3 Hz, NCH3), 48.8 (t, JCH =
129.9 Hz, NCH2-bridge), 41.8 (q, JCH = 131.8 Hz, PhN(CH3)2), 24.4 (t, JCH = 133.1 Hz, β-C
Py), 21.7 (q, JCH = 125.4 Hz, CCH3). 19F NMR (470 MHz, THF-d8, δ): -133.1 (d, JFF = 8.7
Hz, o-F-C6F5), -165.2 (t, JFF = 20.3 Hz, m-F-C6F5), -168.7 (t, JFF = 17.7 Hz, p-F-C6F5).
In situ Generation of [(L6)La(THF-d8)x][B(C6F5)4]2 on an NMR-tube scale. THF-d8
(0.6 mL) was added to a mixture of (L6)La(CH2Ph)2 (28, 8.6 mg, 15 μmol) and
[PhMe2NH][B(C6F5)4] (12.0 mg, 15 μmol) and the suspension was homogenized by
agitation. The resulting solution was transferred to an NMR tube equipped with a Teflon
Young valve and analyzed by NMR spectroscopy, which indicated a clean formation of the
corresponding dicationic species [(L6)La(THF-d8)x][B(C6F5)4]2, 2 equiv of toluene, and free
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
151
PhNMe2. 1H NMR (500 MHz, THF-d8) δ: 3.20 (m, 2H, NCH2), 3.17 (t, 2H, JHH = 5.6 Hz,
NCH2-bridge), 3.14 (d, 2H, JHH = 12.3 Hz, CCH2), 3.08 (t, 2H, JHH = 5.6 Hz, NCH2-bridge),
2.96 (m, 2H, NCH2), 2.94 (m, 4H, α-H Py), 2.93 (d, 2H, JHH = 12.3 Hz, CCH2), 2.62 (s, 6H,
NCH3), 1.99 (m, 4H, β-H Py), 0.84 (s, 3H, CCH3). 13C NMR (125.7 MHz, THF-d8) δ: 150.3
(d, JCF = 242.1 Hz, o-C C6F5), 140.3 (d, JCF = 236.3 Hz, p-C C6F5), 138.4 (d, JCF = 245.4 Hz,
m-C C6F5), 126.3 (b, ipso-C C6F5), 78.5 (t, JCH = 132.7 Hz, CCH2), 62.1 (s, CCH3), 59.1 (t,
JCH = 132.5 Hz, NCH2-bridge), 58.8 (t, JCH = 134.6 Hz, NCH2), 53.8 (t, JCH = 138.7 Hz,
α-C Py), 50.0 (q, JCH = 136.3 Hz, NCH3), 48.5 (t, JCH = 132.5 Hz, NCH2-bridge), 24.8 (t,
JCH = 135.5 Hz, β-C Py), 20.6 (q, JCH = 127.8 Hz, CCH3).
In situ Generation of [(L6)La(C≡CPh)(THF-d8)x][B(C6F5)4] on an NMR tube scale.
Method A: THF-d8 (0.5 mL) was added to a mixture of (L6)La(CH2Ph)2 (28, 17.1 mg, 30
μmol) and [PhNMe2H][B(C6F5)4] (23.8 mg, 30 μmol) and the mixture was homogenized by
agitation. Then the resulting solution was treated with phenylacetylene (3.1 mg, 30 μmol).
The solution was transferred to an NMR tube equipped with a Teflon Young valve and
analyzed by NMR spectroscopy, which indicated a clean conversion to the cationic
monoalkynyl species, toluene, and free PhNMe2. Method B: The dicationic species
[(L6)La(THF-d8)x][B(C6F5)4]2 (in situ generated by reacting (L6)La(CH2Ph)2 (28, 8.4 mg,
15 μmol) with [PhNMe2H][B(C6F5)4] (24.0 mg, 30 μmol) in THF-d8) was treated with
[(L6)La(C≡CPh)(μ-C≡CPh)]2 (42, 8.9 mg, 7.5 μmol) in THF-d8. The resulting solution was
analyzed by NMR spectroscopy, which indicated a clean formation of the cationic
monoalkynyl species [(L6)La(C≡CPh)(THF-d8)x][B(C6F5)4]. 1H NMR (500 MHz, THF-d8)
δ: 7.25-7.05 (m, 5H, Ph), 3.34 (m, 2H, NCH2), 3.14 (m, 2H, NCH2-bridge), 3.13 (m, 4H,
α-H Py), 2.93 (m, 2H, NCH2-bridge), 2.92 (d, 2H, JHH = 11.5 Hz, CCH2), 2.65 (s, 6H,
NCH3), 2.64 (m, 2H, NCH2), 2.57 (d, 2H, JHH = 11.5 Hz, CCH2), 1.99 (m, 4H, β-H Py),
0.83 (s, 3H, CCH3). 13C NMR (125.7 MHz, THF-d8) δ: 160.5 (LaC≡CPh), 150.3 (d, JCF =
242.1 Hz, o-C C6F5), 140.3 (d, JCF = 236.3 Hz, p-C C6F5), 138.4 (d, JCF = 245.4 Hz, m-C
C6F5), 132.8 (dt, JCH = 159.6 Hz, JCH = 6.9 Hz, o-C Ph), 129.9 (dd, JCH = 159.1 Hz, JCH =
8.1 Hz, m-C Ph), 127.3 (dt, JCH = 159.9 Hz, JCH = 7.1 Hz, p-C Ph), 126.3 (b, ipso-C-C6F5),
105.6 (LaC≡CPh), 76.8 (t, JCH = 135.4 Hz, CCH2N), 61.9 (s, CCH3), 59.5 (t, JCH = 133.8
Hz, NCH2-bridge), 59.4 (t, JCH = 135.3 Hz, NCH2), 55.1 (t, JCH = 139.8 Hz, α-C Py), 52.1
(q, JCH = 135.9 Hz, NCH3), 49.1 (t, JCH = 128.0 Hz, NCH2-bridge), 24.8 (t, JCH = 132.9 Hz,
β-C Py), 21.7 (q, JCH = 125.8 Hz, CCH3). 19F NMR (376.3 MHz, THF-d8, δ): -133.1 (d, JFF
= 10.8 Hz, o-F-C6F5), -165.3 (t, JFF = 20.2 Hz, m-F-C6F5), -168.8 (t, JFF = 17.7 Hz,
p-F-C6F5).
Reaction of [(L6)La(C≡CPh)(μC≡CPh)]2 with [PhNMe2H][B(C6F5)4] on an
NMR-tube scale. THF-d8 (0.5 ml) was added to a mixture of [(L6)La(C≡CPh)(μC≡CPh)]2
(19.1 mg, 16.1 μmol) and [PhNMe2H][B(C6F5)4] (25.8 mg, 32.2 μmol) and the mixture was
homogenized by agitation. The resulting solution was transferred to an NMR tube equipped
with a Teflon (Young) valve and analyzed by NMR spectrometry, which indicated to a
Chapter 6
152
clean formation of the cationic dialkynyl species [(HL6)La(C≡CPh)2][B(C6F5)4]. 1H NMR
(500 MHz, THF-d8) δ: 7.20-7.05 (m, 10H, Ph), 3.88 (dd, JHH = 12.3 Hz, JHH = 3.4 Hz, 1H,
NH), 3.68 (m, 1H, NCH2-bridge), 3.25 (m, 1H, NCH2), 3.20 (d, JHH = 13.1 Hz, 1H, CCH2),
3.15 (m, 1H, NCH2), 3.11 (d, JHH = 13.8 Hz, 1H, CCH2), 3.07 (s, 3H, NCH3), 3.06 (m, 2H,
NCH2-bridge), 2.88 (m, 1H, NCH2), 2.84 (d, JHH = 13.8 Hz, 1H, CCH2), 2.78 (m, 1H,
NCH2), 2.72 (s, 3H, NCH3), 2.59 (m, 1H, NCH2-bridge), 2.56 (d, JHH = 13.1 Hz, 1H,
CCH2), 1.99 (m, 4H, β-H Py), 1.12 (s, 3H, CCH3). 13C NMR (125.7 MHz, THF-d8) δ: 159.7
(s, LaC≡CPh), 150.3 (d, JCF = 242.1 Hz, o-C-C6F5), 140.3 (d, JCF = 236.3 Hz, p-C-C6F5),
138.4 (d, JCF = 245.4 Hz, m-C-C6F5), 132.8 (d, JCH = 161.4 Hz, o-C Ph), 129.9 (dd, JCH =
160.1 Hz, JCH = 6.5 Hz, m-C Ph), 129.1 (br, ipso-C Ph), 127.7 (d, JCH = 160.8 Hz, p-C Ph),
126.3 (b, ipso-C-C6F5), 107.5 (br, LaC≡CPh),77.1 (t, JCH = 134.4 Hz, CCH2N), 63.1 (t, JCH
= 135.7 Hz, CCH2N), 60.3 (s, CCH3), 59.9 (t, JCH = 138.2 Hz, NCH2), 59.2 (t, JCH = 137.0
Hz, NCH2), 56.5 (t, JCH = 137.0 Hz, NCH2-bridge), 52.5 (q, JCH = 135.2 Hz, NCH3), 52.0 (q,
JCH = 137.5 Hz, NCH3), 42.8 (t, JCH = 136.9 Hz, NCH2-bridge), 24.8 (t, JCH = 136.6 Hz, Py
β-C), 21.1 (q, JCH = 127.3 Hz, CCH3).
In situ Generation of [(L16)Y(CH2Ph-p-Me)2][B(C6F5)4] (48) on an NMR-tube Scale.
A solution of Y(CH2Ph-p-Me)3(THF)3 (31.0 mg, 50μmol) in C6D6 (0.6 mL) was added to
L16 (13.4 mg, 50 μmol) and the resulting mixture was transferred to an NMR tube equipped
with a Teflon (Young) valve. Then all the volatiles were removed under reduced pressure. A
suspension of [PhNMe2H][B(C6F5)4] (40.0 mg, 50 μmol) in C6D5Br (0.6 mL) was added to
this NMR tube and the mixture was analyzed by NMR spectroscopy. The 1H and 13C{1H}NMR spectra indicated a clean conversion to the title complex, free PhNMe2 and
p-xylene. 1H NMR (500 MHz, C6D5Br) δ: 7.01 (d, JHH = 7.88 Hz, 2H, Ph), 6.90 (d, JHH =
7.84 Hz, 2H, Ph), 6.79 (d, JHH = 7.88 Hz, 2H, Ph), 6.71 (d, JHH = 7.88 Hz, 2H, Ph), 2.96 (m,
1H, NCH2), 2.70 (m, 1H, α-H Py), 2.59 (m, 1H, NCH2), 2.54 (m, 1H, NCH2), 2.47 (m, 2H,
CCH2 + NCH2-bridge), 2.42 (m, 1H, NCH2-bridge), 2.31 (m, 1H, α-H Py), 2.30 (m, 1H,
NCH2), 2.24 (m, 1H, NCH2-bridge), 2.24 (s, 3H, PhCH3), 2.11 (s, 3H, PhCH3), 2.02 (s, 3H,
NCH3), 2.00 (s, 3H, NCH3), 1.93 (s, 3H, NCH3), 1.84 (m, 1H, NCH2), 1.81 (m, 1H, NCH2),
1.80 (m, 1H, α-H Py), 1.69 (m, 1H, NCH2), 1.66 (m, 1H, NCH2-bridge), 1.65 (m, 1H,
YCH2), 1.63 (m, 1H, YCH2), 1.59 (m, 2H, β-H Py), 1.56 (m, 1H, YCH2), 1.52 (m, 2H, β-H
Py), 1.41 (m, 1H, α-H Py), 1.36 (m, 1H, YCH2), 0.35 (s, 3H, CCH3). JYH is not resolved due
to overlap. 13C{1H} (125.7 MHz, C6D5Br) δ: 148.5 (ipso-C Ph), 146.5 (ipso-C Ph), 132.2
(p- or m-C Ph), 128.9 (p- or m-C Ph), 123.6 (p- or m-C Ph), 122.3 (p- or m-C Ph), 68.8
(CCH2), 65.9 (CCH2), 61.2 (CCH3), 58.9 (d, JYC = 41.4 Hz, YCH2), 58.8 (NCH2), 57.7 (α-C
Py), 55.4 (d, JYC = 25.3 Hz, YCH2), 55.2 (NCH2), 53.8 (NCH2), 52.0 (α-C Py), 49.0
(NCH3), 48.5 (NCH3), 47.8 (NCH2-bridge), 35.7 (NCH3), 22.1 (β-C Py), 21.3 (β-H Py),
20.7 (PhCH3), 20.3 (PhCH3), 11.4 (CCH3). The resonances of p-C of p-xylene are obscured
by the resonances of C6D5Br and PhNMe2.
Synthesis of (L6)La[N(SiMe3)2]2 (49). A solution of La[N(SiMe3)2]3 (155.0 mg, 0.25
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
153
mmol) in THF (4 mL) was added to HL6 (63.6 mg, 0.25 mmol) and the resulting solution
was refluxed for 30 h while stirring. All the volatiles were removed under reduced pressure
and the residue was purified by recrystallization from pentane, yielding the title compound
(153.3 mg, 0.22 mmol, 86%) as a colorless crystalline solid (including crystals suitable for
X-ray analysis). 1H NMR (400MHz, C6D6) δ: 3.18 (m, 2H, NCH2), 3.04 (br, 2H,
NCH2-bridge), 2.91 (t, 2H, JHH = 5.6 Hz, NCH2-bridge), 2.61 (m, 4H, α-H Py), 2.54 (d, 2H,
JHH = 12.1 Hz, CCH2), 2.21 (s, 6H, NCH3), 1.98 (m, 2H, NCH2), 1.95 (d, 2H, JHH = 12.1 Hz,
CCH2), 1.47 (m, 4H, β-H Py), 0.75 (s, 3H, CCH3), 0.43 (s, 36H, Si(CH3)3). 13C NMR
(100.5 MHz, C6D6) δ: 69.4 (t, JCH = 132.9 Hz, CCH2N), 61.3 (s, CCH3), 57.1 (t, JCH = 132.1
Hz, α-C Py), 55.2 (t, JCH = 135.9 Hz, NCH2-bridge), 54.2 (t, JCH = 137.8 Hz, NCH2), 49.3
(q, JCH = 134.0 Hz, NCH3), 45.3 (t, JCH = 130.1 Hz, CH2-bridge), 23.6 (q, JCH = 125.1 Hz,
CCH3), 22.5 (t, JCH = 131.6 Hz, β-C Py), 5.9 (q, JCH = 116.1 Hz, Si(CH3)3). Anal. Calc for
C26H65LaN6Si4: C, 43.79; H, 9.19; N, 11.79. Found: C: 43.75; H, 9.22; N, 11.57.
General Procedure for Catalytic Dimerization of Terminal alkynes by {HL6 +
La[N(SiMe3)2]3]} on an NMR-tube scale. (A) Catalyst stock solution preparation: To a
solution of of La[N(SiMe3)2]3 (62.0 mg, 0.1 mmol) in C6D6 (3 mL), was added the solution
of HL6 (25.4 mg, 0.1 mmol) in C6D6 (1 mL). The resulting mixture was homogenized by
agitation and transferred to a 5-mL volumetric flask and C6D6 was added to make the
volume of the solution to 5 mL. The stock solution ([La] = 20.0 μmol) was stored in the
glove box at room temperature. (B) Procedure for dimerization reactions: The catalyst stock
solution (500 μmL) and the substrate a-f (0.5 mmol, 50 equiv) were mixed and transferred
to an NMR tube equipped with a Teflon Young valve. The disappearance of the substrate
and formation of the product can be conveniently followed by NMR. The final volume of
the reaction mixture is approximately 550 μml (500μmL stock solution + ~50μmL substrate)
and [La] is ~18.2 mM.
Structure Determinations of Compounds 40-44, 46, and 49. These measurements
were performed according to the procedure described for 1 in Chapter 2. Crystallographic
data and details of the data collections and structure refinements are listed in Table 6.8 (for
40-43) and Table 6.9 (for 44, 46, and 49).
Chapter 6
154
Table 6.8. Crystal Data and Collection Parameters of Complexes 40-43.
compound 40 41 42 43.0.5(C6H14)
formula C30H39N4Sc C33H46N4Y C60H78N8La2 C38H45N4Sc
Fw 500.62 587.66 1189.14 602.76
cryst color, habit colorless, block colorless, block colorless, block colorless, block
cryst size (mm) 0.39 0.26 0.23 0.39 0.33 0.28 0.22 0.19 0.16 0.55 0.49 0.37
cryst syst monoclinic monoclinic monoclinic monoclinic
space group P21/c P21/n P21/n P21/c
a (Å) 10.8798(17) 12.682(2) 13.8365(16) 19.707(2)
b (Å) 12.3577(19) 14.790(3) 14.4305(16) 26.245(3)
c (Å) 21.351(3) 15.914(3) 14.2150(16) 14.0235(16)
(deg)
(deg) 101.561(2) 93.154(3) 92.3806(17) 90.1905(19)
(deg)
V (Å3) 2812.4(7) 2980.4(9) 2835.8(6) 7253.1(14)
Z 4 4 4 8
calc, g.cm-3 1.182 1.310 1.393 1.104
µ(Mo Kα), cm-1 2.86 19.85 15.3 2.32
F(000), electrons 1072 1244 1216 2576
θ range (deg) 2.52, 26.02 2.52, 26.02 2.46, 26.02 2.91, 26.02
Index range (h, k, l) ±13, ±15, -26:23 ±15, -16:18, ±19 ±17, ±17, ±17 ±17, 0:32, 0:17
Min and max transm 0.8846, 0.9364 0.4512, 0.5737 0.7042, 0.7828 0.8702, 0.9191
no. of reflns collected 20542 21840 21350 14273
no. of reflns collected 5501 5856 5585 14273
no. of reflns with F0 ≥ 4 σ (F0) 3313 3504 4139 10069
wR(F2) 0.1645 0.1216 0.0964 0.1448
R(F) 0.0577 0.0492 0.0411 0.0535
weighting a, b 0.0757, 0 0.0466, 0 0.0478, 0 0.0833, 0
Goof 1.051 0.984 0.974 1.029
params refined 319 347 319 781
min, max resid dens -0.35, 0.25(5) -0.66, 0.70(12) -0.84, 1.37(13) -0.22, 0.40(6)
T (K) 222(1) 100(1) 100(1) 100(1)
Catalytic Dimerization of Terminal Alkynes by Rare Earth Metal Benzyl Complexes
155
Table 6.9. Crystal Data and Collection Parameters of Complexes 44, 46, and 49.
compound 44 46 49
formula C45H53N4Y BC56H84N4O3Y C26H65LaN6Si4
Fw 738.82 1081.14 713.09
cryst color, habit yellow, needle colorless, platelet colorless, platelet
cryst size (mm) 0.36 0.14 0.12 0.49 0.33 0.07 0.44 0.23 0.06
cryst syst monoclinic triclinic monoclinic
space group P21/c P-1 C2/c
a (Å) 12.244(2) 13.740(3) 34.296(2)
b (Å) 18.518(3) 14.401(3) 11.5700(7)
c (Å) 17.670(3) 15.283(4) 19.8130(12)
(deg) 89.564(4)
(deg) 106.915(2) 74.857(3) 107.1781(10)
(deg) 87.564(4)
V (Å3) 3833.2(11) 2916.4(12) 7511.2(8)
Z 4 2 8
calc, g.cm-3 1.280 1.231 1.261
µ(Mo Kα), cm-1 15.58 10.49 12.88
F(000), electrons 1560 1152 3008
θ range (deg) 2.51, 27.56 2.79, 24.11 2.49, 28.28
Index range (h, k, l) ±15, -24:22, ±22 ±15, ±16, ±17 ±45, ±15, ±26
Min and max transm 0.6039, 0.8351 0.6081, 0.9292 0.5084, 0.6536
no. of reflns collected 32731 18305 33190
no. of reflns collected 8782 9093 9313
no. of reflns with F0 ≥ 4 σ (F0) 5112 4816 7981
wR(F2) 0.1155 0.1457 0.0762
R(F) 0.0514 0.0617 0.0312
weighting a, b 0.0255, 2.3578 0.0520, 0 0.0409, 3.90
Goof 1.007 0.962 1.064
params refined 451 679 355
min, max resid dens -0.38, 0.58(8) -0.48, 0.70(8) -0.38, 1.85(9)
T (K) 100(1) 100(1) 100(1)
Chapter 6
156
6.8 References
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Chapter 6
158
Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from the Me3DAPA moiety
159
Chapter 7 Rare Earth Organometallics with Dianionic
Tetradentate Ligands Derived from the Me3DAPA moiety
7.1 Introduction
Dianionic linked cyclopentadienyl-amido ancillary ligands have been successfully used in both transition metal and rare earth metal organometallic chemistry. In
particular, cationic group 4 metal alkyl species like {[(C5Me4)SiMe2NR]M(alkyl)}+
(J),1 have proven to be highly efficient catalysts for the (co-)polymerization of olefins.
Neutral rare earth metal organometallics (Me4CpSiMe2NR)M(alkyl)(THF)x (K) (M = trivalent rare earth metal) also exhibit catalytic properties for a range of
transformations,2 such as olefin polymerization,3 the hydroamination4 and hydrosilylation of alkenes,5 dimerization of alkynes,6 addition of alkyne C-H, amine
N-H, and phosphine P-H bonds carbodiimides,7 and cross-coupling of terminal alkynes with isocyanides.8 Tetradentate nitrogen-based ligands dianionic ligands that are ‘hard
donor’ analogues to these dianionic cyclopentadienyl-amido ancillary ligands, have not been reported thus far.
In earlier chapters, we have shown that 1,4,6-trimethyl-1,4-diazpan-6-amine (Me3DAPA) moiety allows access to a range of neutral and monoanionic ancillary
ligands. This framework also allows facile synthesis of potentially dianionic ligands
like H2L13, H2L
14, and H2L15, that have two secondary amine functionalities that are
readily deprotonated and a substituent on the pendant amido nitrogen that is easily varied (their synthesis is described in Chapter 2). These ligands allowed us to access
neutral rare earth metals monoalkyl complexes of type (L).
Chart I. Ligands Employed in This Chapter
Chapter 7
160
In this chapter, we describe the application of tetradentate dianionic ligands L13-L15 derived from Me3DAPA framework to the synthesis of scandium and yttrium monoalkyl and lanthanum monobenzyl complexes. The prepared complexes were
studied as catalysts for the dimerization of phenylacetylene and it is shown that the ancillary ligand and metal ion size have considerable influences on the rate of
conversion.
7.2 Organo Rare Earth Metal Complexes Supported by Tetradentate
Dianionic Ligands Derived form the Me3DAPA moiety
7.2.1 Synthesis and Characterization of Scandium and Yttrium Monoalkyl Complexes (L)M(CH2SiMe3)(THF)
Reaction of the ligand precursor H2L with one equiv of group 3 metal trialkyls
M(CH2SiMe3)(THF)29 in pentane solvent afforded the monoalkyl complexes
(L)M(CH2SiMe3)(THF) (L = L13, M = Sc, 50; L = L13, M = Y, 51; L = L14, M = Y, 52; L =
L15, M = Y, 53) (Scheme 7.1). They were isolated as off-white crystalline materials after
recrystallization from toluene/n-hexane (for 50, 52, and 53) or THF/n-hexane (51) in
around 70% yield. When performed in C6D6, these reactions were seen by NMR
spectroscopy to be quantitative. The scandium complex 50 could be converted to THF free
complex (L13)Sc(CH2SiMe3) by pumping its toluene solution to dryness. When the isolated
yttrium complex 51 is dissolved in C6D6, it decomposes into a complicated mixture of
ill-defined species. Apparently it needs the presence of some additional THF to be stable in
solution. In contrast, yttrium complexes 52 and 53 are stable in C6D6 for at least two days.
Apparently, the increased steric shielding by the tert-Bu and 2,6-iPr2C6H3 substituents on
the pendant amido group in 52 and 53 sufficiently improves the stability relative to the i-Pr
substituent in 51.
Scheme 7.1. Synthesis of Scandium and Yttrium Monoalkyl Complexes.
1H NMR spectra of these monoalkyl complexes in THF-d8 indicate (averaged) C2v
symmetrical structures, showing that rearrangement around the metal center is fast on the
Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from the Me3DAPA moiety
161
NMR time-scale. The resonances of MCH2 (THF-d8, 23 ºC) for 50 are found at δ -1.26 ppm
(1H) and δ 22.9 ppm (13C), and for 51 at δ -1.46 ppm (d, JYH = 2.3 Hz) and δ 23.2 ppm (JYC
= 31.4 Hz, JCH = 97.0 Hz), respectively. Their ambient-temperature 1H NMR spectra in
toluene-d8 show broad signals, indicating fluxionality. Cooling the toluene-d8 solution of 52
and 53 to -50 ºC slows this dynamic process, revealing fully asymmetric structures. The 1H
NMR spectrum of 52 shows a single resonance (δ -1.29 ppm; 13C, δ -1.29 ppm, JYC = 29.8
Hz) for the two YCH2 protons, whereas for 53 two doublets are seen (δ -1.18 and -1.34 ppm,
JHH = 10.4 Hz, JYH not resolved; 13C δ 21.7 ppm, JYC = 32.0 Hz). This suggests that, in
toluene-d8, the complex with the less sterically demanding substituent on the pendent amido
nitrogen more readily inverts the configuration of the metal center (the tert-butyl group in
52 is smaller than the2,6-iPr2C6H3 group in 53).
Figure 7.1. Structures of Complexes 50 (up) and 51 (bottom). All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
The structures of 50, 51, and 53 were established by single-crystal X-ray diffraction and
are shown in Figure 7.1 (for 50 and 51) and Figure 7.2 (for 53) (the geometric data are
compiled in Table 7.1). All the three complexes show a distorted octahedral geometry
around the metal center, with the three nitrogen atoms of the 1,4-diazepan-6-amido moiety
in a fac-arrangement. For each of these three complexes, the three nitrogen atoms N(1),
N(3), and N(4) coordinate to the metal center in a mer fashion. These three nitrogen atoms
and the metal center are essentially coplanar since the angle N(1)-M-N(4) is equal to the
sum of angles N(1)-M-N(3) and N(3)-M-N(4). Each metal center in these complexes
displays two short M-N bonds (M-N(3) and M-N(4)) and two longer M-N bonds (M-N(1)
and M-N(2)), consistent with diamido-diamino ligand character. The geometry around the
amido N(4) is essentially planar (the sum of angles ΣN(4) is 360º); the geometry around the
amido N(3) deviates significantly from planarity: this amido nitrogen is pyramidalized with
one electron lone pair available for coordination (the sum of angles ΣN(3) is 349.5(2)º,
337.97(19)º, and 344.1(3)º for 50, 51, and 53, respectively). This indicates that these two
amido nitrogen atoms N(3) and N(4) are 2e and 4e donors respectively, thus these
monoalkyl complexes can be best described as neutral 14e species.
Chapter 7
162
Figure 7.2. Structure of Complexes 53. All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Table 7.1. Geometrical Data of Compounds 50, 51, and 53.
50 (M = Sc) 51 (M = Y) 53 (M = Y)
Bond lengths (Å) M-N(1) 2.400(3) 2.576(2) 2.675(4)
M-N(2) 2.522(2) 2.579(2) 2.576(4) M-N(3) 2.118(2) 2.279(2) 2.260(4)
M-N(4) 2.057(2) 2.214(2) 2.265(3) M-O 2.2077(19) 2.364(2) 2.353(3)
M-C(14) 2.318(4) 2.521(3) 2.509(4) Bond angles (deg)
N(1)-M-N(3) 75.34(8) 70.94(8) 71.72(12) N(3)-M-N(4) 74.90(9) 70.88(8) 69.64(11)
N(1)-M-N(3) + N(3)-M-N(4) 150.24(9) 141.82(8) 141.36(12) N(1)-M-N(4) 150.24(9) 141.81(8) 141.33(12)
ΣN(3) 349.5(2) 337.97(19) 344.1(3) ΣN(4) 359.9(2) 359.99(18) 360.0(3)
The two amido nitrogen atoms in 50 and 51 are unequally bound to the metal center and
M-N(3) bond is longer than M-N(4) bond by 0.061(2) Å and 0.065(2) Å for 50 and 51,
respectively; whereas the two M-N(amido) bonds in 53 are almost identical (Y-N(3) =
2.260(4) Å and Y-N(4) = 2.265(3) Å). The two amino nitrogen atoms in 50 bind to
scandium asymmetrically (Sc-N(1) = 2.400(3) Å and Sc-N(2) = 2.522(2) Å), while the two
amino nitrogen atoms in 51 bind to the yttrium center with equal bond distances (Y-N(1) =
2.576(2) Å and Y-N(2) = 2.579(2) Å); this indicates that there is more strain imposed on the
Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from the Me3DAPA moiety
163
ligand L13 by coordination of all four nitrogen atoms to the smaller scandium in 50 than to
the larger metal yttrium. The Y-N(4) distance in 51 is 0.051 Å shorter than that in 53; this
suggests that the isopropyl group is less sterically demanding than the 2,6-iPr2C6H3 group,
thus brings the nitrogen N(4) closer to the yttrium center in 52. In line with this, the angle
C(11)-N(4)-Y in 52 (143.35(17)º) is larger than the corresponding angle (138.7(3)º) in 53.
As described above, one of the amido nitrogen atoms has its electron lone pair apparently
free and available in these monoalkyl complexes. In chapter 6, we have shown that the
amido nitrogen atom in the dialkynyl complexes 40-42 is able to accept a proton from
phenylacetylene, forming the trialkynyl complexes with a coordinated secondary amine
ligand functionality. To see whether the amido nitrogen atom can donate its electron lone
pair to other metals, the yttrium monoalkyl complex 53 was reacted with 1 equiv of
LiCH2SiMe3 in C6D6 and this afforded a single organometallic species. A single-crystal
X-ray diffraction study on the isolated material (Figure 7.3, with the geometric data
compiled in Table 7.2) showed that it can be formulated as
{η3:η1-[(Me3DAPA)SiMe2N(2,6-iPr2C6H3)]Y(CH2SiMe3)}{[μ-(CH2SiMe3), μ-η1-N]Li(THF)}
(54, Scheme 7.2). On a preparative scale, 54 was obtained (isolated yield: 81%) as a
colorless solid after crystallization from a toluene/hexane mixture. The structure of 54
reveals a hetero-bimetallic complex with a six-coordinate octahedral yttrium center and a
three-coordinate essentially planar lithium center (the sum of angles around ΣLi is
358.0(2)º), bridged by a nitrogen atom and an alkyl group. The geometry around the
yttrium center of 54 does not differ significantly from that of 53 and the position taken by
the coordinated THF molecule in 53 is occupied by a bridging alkyl group with the angle
Y-C(27)-Si(3) of 178.2(2)º in 54. The distances of the two Y-C bonds for the terminal and
bridging alkyl groups does not differ significantly (Y-C(23) = 2.480(4) Å and Y-C(27) =
2.470(3) Å). The difference of 0.085 Å between the two Y-N(amido) bond distances in 54 is
larger than that in 53 (0.005 Å). Thus, the electron lone pair on the amido N(3) in 53 is
available for binding the Lewis acid cation Li+.
Scheme 7.2. Reaction of 53 with LiCH2SiMe3.
The low-temperature solution NMR spectra of 54 in toluene-d8 (-50 º) are consistent with
the structure as determined by X-ray diffraction. The 1H spectrum indicates a fully
asymmetric structure, as seen e.g. by two methyl resonances for the NMe-groups (δ 2.44
Chapter 7
164
and 2.26 ppm) and the SiMe2-group (δ 0.23 and -0.04 ppm), and four methyl resonances for
the two isopropyl groups (δ 1.59, 1.57, 1.49, and 1.33 ppm). The YCH2 protons are
diastereotopic and their resonances are found at -0.59 and -1.10 ppm (JHH = 10.7 Hz, JYH
not resolved) for the terminal alkyl group and at -0.51 and -1.21 ppm (JHH = 7.2 Hz, JYH not
resolved) for the bridging alkyl group, with the corresponding 13C resonances at 23.1 ppm
(JYC = 33.3 Hz) and 27.7 ppm (JYC = 27.8 Hz), respectively.
Figure 7.3. Molecular Structure of 54. All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Table 7.2. Geometrical Data of Complex 54.
Bond Length (Å)
Y-N(1) 2.598(3) Y-N(3) 2.345(3)
Y-N(2) 2.635(3) Y-N(4) 2.260(2)
Li-N(3) 2.039(5) Li-O(1) 1.926(5) Y-C(23) 2.480(4) Li-C(27) 2.269(5)
Y-C(27) 2.470(3) Bond Angles (deg)
N(2)-Y-N(3) 71.13(8) Y-C(23)-Si(2) 124.88(16) N(3)-Y-N(4) 69.63(9) Y-C(27)-Si(3) 178.2(2)
N(2)-Y-N(4) 140.64(10) Li-C(27)-Si(3) 100.9(2)
7.2.2 Synthesis and Characterization of Lanthanum Monobenzyl Complexes (L)La(CH2Ph)(THF) (L = L14 and L15).
Reaction of ligand precursors H2L with one equiv of the lanthanum tribenzyl starting
material La(CH2Ph)3(THF)310 in THF afforded monobenzyl complexes (L)La(CH2Ph)(THF)
(L = L14, 55; L = L15, 56) as shown in Scheme 7.3. They were obtained (isolated yields: 55,
67%; 56, 80%) as yellow crystalline materials after crystallization from THF/n-hexane. The
Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from the Me3DAPA moiety
165
LaCH2 resonances for 55 are found at δ 2.38 ppm (1H) and δ 59.5 ppm (13C), for 56 at δ 2.13
ppm and δ 63.4 ppm respectively.
Scheme 7.3. Synthesis of Lanthanum Monobenzyl Complexes.
Figure 7.3. Molecular structure of 55. All hydrogen atoms are omitted for clarity and thermal
ellipsoids are drawn at the 30% probability level.
Table 7.3. Geometrical Data of Complex 55.
Bond Length (Å)
La-N(1) 2.766(3) La-N(3) 2.345(3) La-N(2) 2.804(3) La-N(4) 2.362(2)
La-C(15) 2.758(5) La-C(16) 2.974(4) Bond Angles (deg)
N(1)-Y-N(3) 68.33(9) N(2)-La-O 140.39(9) N(3)-Y-N(4) 65.51(10) La-C(15)-C(16) 84.4(3)
N(1)-Y-N(4) 133.02(10)
Complex 55 was characterized by single-crystal X-ray diffraction and its structure is
shown in Figure 7.4, with the geometric data compiled in Table 7.3. The structure
Chapter 7
166
determination of 55 at 100K was complicated by the occurrence of a low-temperature phase
transition, causing splitting of the diffraction peaks. To avoid this problem, data collection
was carried out at 222K, resulting in successful structural characterization, but a lower
accuracy due to increased thermal motion of the atoms. This complex features a 7-coordinate
lanthanum center with the coordination sphere composed of four nitrogen atoms of L14, one
THF, and one η2-benzyl group. Ligand L14 coordinates to lanthanum in almost the same way
as L13 and L15 to the yttrium center in 51 and 53. The lanthanum center display two long
La-N(amino) bonds (La-N(1) = 2.766(3) Å and La-N(2) = 2.804(3) Å) and two short
La-N(amido) bonds (La-N(3) = 2.345(3) Å and La-N(4) = 2.362(3) Å), consistent with the
diamino-diamido ligand character. The geometry around amido N(4) is planar (the sum of
angles ΣN(4) is 359.9(3)º) and the other amido N(3) deviates from planar geometry (the
sum of angles ΣN(3) is 350.3(2)º). The benzyl group is η2-bound to the lanthanum center
with La-C(15) = 2.758(5) Å, La-C(16) = 2.974(4) Å and La-C(15)-C(16) = 84.4(3)º.
Table 7.4. Catalytic Dimerization of Phenylacetylene by the Scandium, Yttrium, and
Lanthanum Monobenzyl Complexes.a
a Reaction conditions: Catalyst (10 μmol), [M] = 18.2 mM, substrate (0.5 mmol), solvent:
C6D6, 80 ˚C; b Conversion and product selectivity are determined by in situ 1H NMR
spectroscopy;
7.3 Catalytic Dimerization of Phenyacetylene
In Chapter 5, we have shown that the neutral dibenzyl complex (L6)La(CH2Ph)2 (28) and
the ionic complex [(L6)Y(CH2Ph)][B(C6F5)4] can effectively and selectively dimerize a
range of (hetero)aromatic terminal alkynes to (Z)-1,4-disubstituted enynes. Here,
dimerization of phenylacetylene was studied with the neutral monoalkyl scandium and
yttrium and monobenzyl lanthanum complexes and the results are listed in Table 7.4. The
scandium complex 50 does not show catalytic activity towards phenyacetylene in C6D6 at 80
entry catalyst time (min) conv. (%)b product select.(%)b
1 50 200 0
2 52 1200 >99 >99
3 53 870 >99 >99
4 55 15 >99 >99
5 56 <5 >99 >99
Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from the Me3DAPA moiety
167
ºC (entry 1). For yttrium and lanthanum the complexes can effectively dimerize
phenylacetylene (50 equiv) to Z-1,4-diphenylbut-1-en-3-yne in benzene solvent with full
conversion and selectivity. Comparing the catalytic activity of the yttrium and lanthanum
complexes bearing the same ancillary ligand L14 (entry 2 and 4) or ligand L15 (entry 3 and 5)
indicates that the complex with the larger ionic radius shows the higher activity. The effect of
the ancillary ligands can be compared on both yttrium (L14, entry 2; L15, entry 3) and
lanthanum (L14, entry 4; L15, entry 5) catalysts; in both cases, the catalyst with ligand L15,
bearing a 2,6-diisopropylphenyl group on the pendant amido nitrogen, is more active than the
corresponding catalyst with L14, bearing a tert-butyl group on the pendant amido nitrogen.
7.4 Concluding Remarks
We have shown that the tetradentate dianionic ligands L13-L15 can be used to prepare rare
earth metal monoalkyl and monobenzyl complexes, and found that the stability of these
complexes depends considerably on the substituent on the pendant amido nitrogen
functionality of these ligands and the size of the metals. The amido-nitrogen attached to the
1,4-diazapane moiety is pyramidalized, and is able to interact through its lone pair with
Lewis acids. In line with this and the proposed pathway for linear Z-selective alkyne
dimerization outlined in chapter 6, the yttrium and lanthanum complexes carrying these
ligands catalyze the dimerization of phenylacetylene with full selectivity to Z-enyne. The
(L15)La-catalyst system is the most active catalyst for this transformation observed thus far.
7.5 Experimental Section
General Remarks. See the corresponding section in Chapter 2. M(CH2SiMe3)3(THF)2
(M = Sc and Y)9 and La(CH2Ph)3(THF)310 were prepared according to the literature
procedures.
Synthesis of (L13)Sc(CH2SiMe3)(THF) (50). To a solution of Sc(CH2SiMe3)3(THF)2
(215.8 mg, 0.48 mmol) in THF (20 ml), was added a solution of H2L13 (130.4 mg, 0.48 mmol)
in THF (10 ml) and the resulting solution was stirred at room temperature for 30 min.
Volatiles were removed under vacuum and the residue was purified by crystallization from
THF/hexane solution to yield the title compound (166.4 mg, 0.35 mmol, 73%) as off-white
crystals. 1H NMR (400 MHz, THF-d8, 23 ˚C, δ): 3.41 (sept, 1H, JHH = 6.2 Hz, CH(CH3)2),
3.30 (br, 2H, CCH2N), 2.90 (br, 2H, NCH2), 2.40-2.54 (br, 10H, NCH2 + CCH2N + NCH3),
1.10 (d, 6H, JHH = 6.3 Hz, CH(CH3)2), 0.85 (s, 3H, CCH3), 0.01 (br, 6H, Si(CH3)2), -0.08 (s,
9H, Si(CH3)3), -1.26 (s, 2H, ScCH2). 13C{1H} NMR (100.6 MHz, THF-d8) δ: 82.3 (CCH2),
60.4 (t, JCH = 137.2 Hz, NCH2), 59.2 (s, CCH3), 51.1 (NCH3), 50.4 (CH(CH3)2), 32.0
(CH(CH3)2), 27.7 (CCH3), 22.9 (ScCH2), 7.5 (Si(CH3)2), 6.3 (Si(CH3)3). Anal. Calcd for
C21H49N4OScSi2: C, 53.13; H, 10.40; N, 11.80. Found: C: 52.74; H, 10.40; N, 11.61.
Synthesis of (L13)Sc(CH2SiMe3) on an NMR Tube Scale. Complex 50 (16.7 mg, 35
Chapter 7
168
μmol) was dissolved in toluene (0.5 mL) and then all the volatiles were removed under
reduced pressure. The residue was dissolved in toluene-d8 (0.5 mL) and the resulting solution
was transferred to an NMR tube equipped with a Teflon Young valve and analyzed by NMR
spectroscopy, which indicated quantitative formation of the THF-free complex. 1H NMR
(500 MHz, toluene-d8, -50 ˚C) δ: 3.80 (sept, 1H, JHH = 6.2 Hz, CH(CH3)2), 3.05 (m, 1H,
NCH2), 2.93 (d, 1H, JHH = 12.0 Hz, CCH2N), 2.71 (m, 1H, NCH2), 2.50 (s, 3H, NCH3), 2.42
(d, 1H, JHH = 11.0 Hz, CCH2N), 2.15 (d, 1H, JHH = 12.0 Hz, CCH2N), 1.92 (d, 1H, JHH = 12.0
Hz, CCH2N), 1.92 (s, 3H, NCH3), 1.82 (m, 2H, NCH2), 1.48 (d, 3H, JHH = 6.2 Hz, CH(CH3)2),
1.46 (d, 3H, JHH = 6.2 Hz, CH(CH3)2), 0.96 (s, 3H, CCH3), 0.52 (s, 3H, Si(CH3)2), 0.41 (s, 3H,
Si(CH3)2), 0.38 (s, 9H, Si(CH3)3), -1.01 (d, 1H, JHH = 10.9 Hz, ScCH2), -1.21 (d, 1H, JHH =
10.9 Hz, ScCH2). 13C{1H} NMR (125.7 MHz, toluene-d8, -50 ˚C) δ: 81.9 (CCH2N), 79.1
(CCH2N), 58.5 (NCH2), 58.1 (NCH2), 57.4 (CCH3), 49.8 (NCH3), 49.3 (NCH3), 49.0
(CH(CH3)2), 31.3 (CH(CH3)2), 31.1 (CH(CH3)2), 26.7 (CCH3), 21.2 (ScCH2), 7.1 (Si(CH3)2),
7.0 (Si(CH3)2), 5.7 (Si(CH3)3).
Synthesis of (L13)Y(CH2SiMe3)(THF) (51). It was made by following the procedure
described for 50. Y(CH2SiMe3)3(THF)2 (248.4 mg, 0.50 mmol) and H2L13 (136.8 mg, 0.50
mmol) were used as starting materials and the same workup procedure gave the title
compound (197.3 mg, 0.38 mmol, 76%) as off-white crystals. 1H NMR (400 MHz, THF-d8,
23 ̊ C, δ): 3.61 (m, 4H, α-H-THF), 3.26 (m, 3H, CH(CH3)2 + CCH2N), 2.80 (d, 2H, JHH = 11.2
Hz, NCH2), 2.59 (d, 2H, JHH = 11.2 Hz, NCH2), 2.57 (m, 2H, CCH2N), 2.53 (s, 6H, NCH3),
1.76 (m, 4H, β-H-THF), 1.09 (d, 6H, JHH = 6.2 Hz, CH(CH3)2), 0.87 (s, 3H, CCH3), -0.05 (s,
6H, Si(CH3)2), -0.09 (s, 9H, Si(CH3)3), -1.46 (d, 2H, JHH = 2.3 Hz, YCH2). 13C NMR (100.6
MHz, THF-d8, 23 ̊ C, δ): 82.7 (t, JCH = 133.4 Hz, CCH2N), 69.5 (t, JCH = 143.7 Hz, α-C-THF),
59.9 (t, JCH = 137.2 Hz, NCH2), 59.3 (s, CCH3), 50.4 (q, JCH = 134.5 Hz, NCH3), 50.0 (d, JCH
= 127.6 Hz, CH(CH3)2), 30.3 (q, JCH = 123.6 Hz, CH(CH3)2), 28.4 (q, JCH = 123.6 Hz, CCH3),
23.2 (dt, JYC = 31.4 Hz, JCH = 97.0 Hz, YCH2), 7.3 (q, JCH = 115.2 Hz, Si(CH3)2), 6.4 (q, JCH
= 116.0 Hz, Si(CH3)3). Anal. Calcd for C21H49N4OSi2Y: C, 48.62; H, 9.52; N, 10.80. Found:
C, 47.86; H, 9.41; N, 10.86.
Synthesis of (L14)Y(CH2SiMe3)(THF) (52). To a solution of Y(CH2SiMe3)3(THF)2
(248.1 mg, 0.50 mmol) in toluene (30 ml), was added a solution of ligand H2L14 (143.7 mg,
0.50 mmol) in toluene (20 ml) and the resulting solution was stirred for 30 min at room
temperature. All volatiles were removed under vacuum and the residue was purified by
recrystallization from a hexane/toluene mixture to give the title compound (199.8 mg, 0.37
mmol, 74%) as a white solid. 1H NMR (500 MHz, toluene-d8, -50 ˚C, δ): 3.81 (br, 2H,
α-H-THF), 3.70 (br, 2H, α-H-THF), 3.05 (br, 1H, NCH2), 2.88 (br, 1H, CCH2N), 2.69 (br, 1H,
NCH2), 2.43 (br, 4H, CCH2N + NCH3), 2.18 (br, 1H, CCH2N), 1.97 (br, 1H, CCH2N), 1.89 (s,
3H, NCH3), 1.83 (br, 2H, NCH2), 1.63 (s, 9H, C(CH3)3), 1.16 (b, 4H, β-H-THF), 1.08 (s, 3H,
CCH3), 0.62 (br, 6H, Si(CH3)2), 0.46 (s, 9H, Si(CH3)3), -1.29 (s, 2H, YCH2). {1H}13C NMR
(125.7 MHz, toluene-d8, -50 ˚C, δ): 81.0 (CCH2N), 78.5 (CCH2N), 71.8 (α-C-THF), 57.5
Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from the Me3DAPA moiety
169
(CCH3), 56.9 (NCH2), 52.4 (C(CH3)3), 48.3 (NCH3), 47.8 (NCH3), 37.4 (C(CH3)3), 26.5
(CCH3) 24.8 (β-C-THF), 20.8 (d, JYC = 29.8 Hz, YCH2), 10.9 (Si(CH3)2), 9.0 (Si(CH3)2), 5.5
(Si(CH3)3). Anal. Calcd for C22H51N4OSi2Y: C, 49.60; H, 9.65; N, 10.52. Found: C, 49.52; H,
9.73; N, 10.29.
Synthesis of (L15)Y(CH2SiMe3)(THF) (53). It was made by following the procedure
described for 50. Y(CH2SiMe3)3(THF)2 (494.7 mg, 1.0 mmol) and H2L3 (390.9 mg, 1.0 mmol)
were used as starting materials and the same workup procedure gave the title compound +
toluene (420.4 mg, 0.66 mmol, 66%) as off-white crystals. 1H NMR (500 MHz, toluene-d8,
-50 ˚C) δ: 7.33 (br, 2H, m-H-Ph), 7.13 (br, 1H, p-H-Ph), 4.18, (br, 1H, CH(CH3)2), 3.96 (br,
1H, CH(CH3)2), 3.92 (br, 2H, α-H-THF), 3.84 (br, 2H, α-H-THF), 3.10 (br, 1H, NCH2), 2.86
(d, 1H, JHH = 11.2 Hz, CCH2N), 2.63 (br, 1H, NCH2), 2.52 (s, 3H, NCH3), 2.40 (d, 1H, JHH =
10.6 Hz, CCH2N), 2.20 (d, 1H, JHH = 11.2 Hz, CCH2N), 1.94 (d, 1H, JHH = 10.6 Hz, CCH2N),
1.79 (m, 2H, NCH2), 1.76 (s, 3H, NCH3) 1.54 (br, 7H, β-H-THF + CHCH3), 1.45, (br, 3H,
CHCH3), 1.20 (br, 3H, CHCH3), 1.11 (br, 3H, CHCH3), 1.03 (s, 3H, CCH3), 0.40 (s, 3H,
SiCH3), 0.33 (s, 3H, SiCH3), 0.23 (s, 9H, Si(CH3)3), -1.18 (d, 1H, JHH = 10.4 Hz, YCH2),
-1.34 (d, 1H, JHH = 10.4 Hz, YCH2). {1H}13C NMR (125.7 MHz, toluene-d8, -50 ˚C) δ: 150.4
(ipso-C-Ph), 141.9 (o-C-Ph), 141.1 (o-C-Ph), 123.0 (m-C-Ph), 122.7 (m-C-Ph), 118.7
(p-C-Ph), 81.9 (CCH2N), 78.0 (CCH2N), 72.0 (α-C-THF), 57.9 (NCH2), 57.4 (CCH3), 56.9
(NCH2), 49.3 (NCH3), 48.6 (NCH3), 27.3 (CHCH3), 27.2 (CHCH3), 27.1 (CHCH3), 27.0
(CHCH3), 26.8 (CCH3), 25.3 (CHCH3), 23.8 (β-C-THF + CHCH3), 21.7 (d, JYC = 32.0 Hz,
YCH2), 7.1 (Si(CH3)2), 5.4 (Si(CH3)2), 5.2 (Si(CH3)3). 1H NMR (500 MHz, THF-d8) δ: 6.84
(d, 2H, JHH = 7.6 Hz, m-H-Ph), 6.55 (t, 1H, JHH = 7.5 Hz, p-H-Ph), 3.85 (septet, 2H, JHH = 6.9
Hz, CH(CH3)2), 3.36 (m, 2H, CCH2N), 2.93 (d, 2H, JHH = 11.4 Hz, NCH2), 2.71 (d, 2H, JHH =
11.4 Hz, NCH2), 2.64 (m, 2H, CCH2N), 2.63 (s, 6H, NCH3), 1.12 (br, 12H, CH(CH3)2), 0.96
(s, 3H, CCH3), -0.08 (s, 6H, Si(CH3)2), -0.24 (s, 9H, Si(CH3)3), -1.46 (d, 2H, JHH = 2.1 Hz,
YCH2). 13C NMR (125.7 MHz, THF-d8) δ: 152.4 (ipso-C-Ph), 143.5 (o-C-Ph), 123.9 (d, JCH
= 149.5 Hz, m-C-Ph), 119.7 (d, JCH = 156.0 Hz, p-C-Ph), 82.3 (t, JCH = 133.6 Hz, CCH2N),
69.4 (t, JCH = 144.3 Hz, α-C-THF), 60.0 (t, JCH = 135.2 Hz, NCH2), 59.7 (s, CCH3), 51.1 (q,
JCH = 135.0 Hz, NCH3), 28.8 (d, JCH = 128.6 Hz, CH(CH3)2), 28.2 (q, JCH = 124.9 Hz,
CH(CH3)2), 27.6 (q, JCH = 132.3 Hz, CCH3), 23.9 (dt, JYC = 32.4 Hz, JCH = 96.9 Hz, YCH2),
7.5 (q, JCH = 115.9 Hz, Si(CH3)2), 6.1 (q, JCH = 115.9 Hz, Si(CH3)3). Anal. Calcd for
C37H67N4OSi2Y: C, 60.96; H, 9.23; N, 7.69. Found: C, 60.52; H, 9.28; N, 7.63.
Synthesis of {η3:η1-[(Me3DAPA)SiMe2N(2,6-iPr2C6H3)]Y(CH2SiMe3)}{[μ-(CH2SiMe3),
μ-η1-N]Li(THF)} (54). To a solution of Y(CH2SiMe3)3(THF)2 (208.1 mg, 0.42 mmol) and
LiCH2SiMe3 (39.6 mg, 0.42 mmol) in toluene (10 ml), was added a solution of H2L3 (164.4
mg, 0.42 mmol) in toluene (5 ml) and the resulting solution was stirred for 30 min at room
temperature. Volatiles were removed under vacuum and the residue was purified by
crystallization from toluene/hexane to give the title compound (242.7 mg, 0.34 mmol, 81%)
as colorless crystals. 1H NMR (500 MHz, toluene-d8, -50 ˚C, δ): 7.29 (br, 2H, m-H-Ph), 7.07
(br, 1H, p-H-Ph), 4.17, (sept, 1H, JHH = 6.6 Hz, CH(CH3)2), 4.08 (sept, 1H, JHH = 6.7 Hz,
Chapter 7
170
CH(CH3)2), 3.28 (m, 4H, α-H-THF), 2.99 (d, 1H, JHH = 12.5 Hz, CCH2N), 2.96 (m, 1H,
NCH2), 2.66 (m, 1H, NCH2), 2.44 (s, 3H, NCH3), 2.26 (s, 3H, NCH3), 1.95 (d, 1H, JHH = 12.9
Hz, CCH2N), 1.87 (d, 1H, JHH = 12.5 Hz, CCH2N), 1.86 (d, 1H, JHH = 12.9 Hz, CCH2N), 1.72
(m, 2H, NCH2), 1.59, (d, 3H, JHH = 6.4 Hz, CHCH3), 1.57 (d, 3H, JHH = 6.4 Hz, CHCH3),
1.49 (d, 3H, JHH = 6.6 Hz, CHCH3), 1.33 (d, 3H, JHH = 6.2 Hz, CHCH3), 1.11 (m, 7H,
β-H-THF), 0.75 (s, 3H, CCH3), ), 0.38 (s, 9H, Si(CH3)3), 0.30 (s, 9H, Si(CH3)3), 0.23 (s, 3H,
SiCH3), -0.04 (s, 3H, SiCH3), -0.51 (d, 1H, JHH = 7.2 Hz, Li(μ-CH2)Y), -0.59 (d, 1H, JHH =
10.7 Hz, YCH2), -1.10 (d, 1H, JHH = 10.7 Hz, YCH2), -1.21 (d, 1H, JHH = 7.2 Hz,
Li(μ-CH2)Y). {1H}13C NMR (125.7 MHz, toluene-d8, -50 ˚C, δ): 149.8 (ipso-C-Ph), 142.1
(o-C-Ph), 141.9 (o-C-Ph), 123.4 (m-C-Ph), 122.9 (m-C-Ph), 119.3 (p-C-Ph), 78.5 (CCH2N),
77.1 (CCH2N), 69.0 (α-C-THF), 58.4 (NCH2), 57.4 (CCH3), 57.2 (NCH2), 52.4 (NCH3), 49.4
(NCH3), 29.0 (CHCH3), 27.8 (CCH3), 27.7 (d, JYC = 27.8 Hz, Li(μ-CH2)Y), 27.3 (CHCH3),
27.1 (CHCH3), 24.9 (β-C-THF), 23.9 (CHCH3), 23.4 (CHCH3), 23.1 (d, JYC = 33.3 Hz,
YCH2), 6.9 (Si(CH3)2), 5.1 (Si(CH3)3), 4.3 (Si(CH3)2), 4.1 (Si(CH3)3). Anal. Calc for
C34H70LiN4OSi3Y: C, 55.86; H, 9.65; N, 7.66. Found: C, 56.46; H, 9.73; N, 7.31.
Synthesis of (L14)La(CH2Ph)(THF) (55). To a solution of La(CH2Ph)3(THF)3 (314.3 mg,
0.5 mmol) in THF (2 ml), was added a solution of ligand H2L14 (143.3 mg, 0.5 mmol) in THF
(2 ml) and the resulting solution was stirred for 15 min at room temperature. All the volatiles
were removed under reduced pressure and the residue was purified by crystallization from
THF/hexane to give the title compound (199.5 mg, 0.34 mmol, 67%) as a yellow crystalline
solid. 1H NMR (400 MHz, C6D6, 23 ˚C, δ): 6.90 (t, 2H, JHH = 7.6 Hz, m-H-Ph), 6.29 (d, 2H,
JHH = 7.6 Hz, o-H-Ph), 6.19 (t, 1H, JHH = 7.1 Hz, p-H-Ph), 3.65 (m, 4H, α-H-THF), 2.55 (m,
2H, NCH2), 2.53 (d, 2H, JHH = 11.7 Hz, CCH2N), 2.38 (s, 2H, LaCH2Ph), 2.15 (d, 2H, JHH =
11.7 Hz, CCH2N), 2.06 (s, 6H, NCH3), 1.87 (m, 4H, NCH2), 1.62 (s, 9H, C(CH3)3), 1.29 (m,
4H, β-H-THF), 1.03 (s, 3H, CCH3), 0.53 (s, 6H, Si(CH3)2). 13C NMR (100.6 MHz, C6D6, 23
˚C, δ): 154.9 (ipso-C-Ph), 131.6 (m-C-Ph), 117.9 (o-C-Ph), 111.5 (p-C-Ph), 78.6 (CCH2N),
70.9 (α-C-THF), 59.5 (LaCH2Ph), 59.5 (CCH3), 57.3 (NCH2), 53.9 (C(CH3)3), 48.1 (NCH3),
36.8 (C(CH3)3), 26.2 (CCH3), 25.4 (β-C-THF), 10.1 (Si(CH3)2).
Synthesis of (L15)La(CH2Ph)(THF) (56). It was synthesized by following the procedure
described for compound 55. Ligand H2L15 (195.3 mg, 0.5 mmol) and La(CH2Ph)3(THF)3
(314.3 mg, 0.5 mmol) were used as starting materials and the title compound (276.2 g, 0.4
mmol, 80%) was isolated as yellow powder. 1H NMR (500 MHz, C6D6, 23 ̊ C, δ): 7.36 (d, 2H,
JHH = 7.5 Hz, m-H-Ph), 7.12 (t, 1H, JHH = 7.5 Hz, p-H-Ph), 6.74 (t, 2H, JHH = 7.5 Hz, m-H-Ph),
6.09 (d, 2H, JHH = 7.5 Hz, o-H-Ph), 6.06 (t, 1H, JHH = 7.2 Hz, p-H-Ph), 4.02 (sept, 2H, JHH =
6.8 Hz, CH(CH3)2), 3.63 (m, 4H, α-H-THF), 2.64 (d, 2H, JHH = 11.7 Hz, CCH2N), 2.57 (m,
2H, NCH2), 2.17 (d, 2H, JHH = 11.7 Hz, CCH2N), 2.13 (s, 2H, LaCH2Ph), 2.08 (s, 6H, NCH3),
1.87 (m, 2H, NCH2), 1.57-1.31 (br, 12H, CH(CH3)2), 1.27 (m, 4H, β-H-THF), 1.02 (s, 3H,
CCH3), 0.40 (s, 6H, Si(CH3)2). 13C NMR (125.7 MHz, C6D6, 23 ˚C, δ): 154.9 (ipso-C-Ph),
150.2 (ipso-C-Ph-ligand), 141.5 (o-C-Ph-ligand), 132.5 (m-C-Ph), 123.1 (m-C-Ph-ligand),
Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from the Me3DAPA moiety
171
118.8 (p-C-Ph-ligand), 117.5 (o-C-Ph), 112.1 (p-C-Ph), 78.4 (CCH2N), 70.4 (α-C-THF), 63.4
(LaCH2Ph), 59.5 (CCH3), 57.2 (NCH2), 48.3 (NCH3), 27.4 (CH(CH3)2), 27.0 (CH(CH3)2),
26.5 (CCH3), 25.4 (β-C-THF), 24.8 (CH(CH3)2), 7.2 (Si(CH3)2). Anal. Calcd for
C33H55LaN4OSi: C, 57.38; H, 8.02; N, 8.11. Found: C, 56.45; H, 7.96; N, 7.80.
Structure Determinations of Compounds 50, 51, and 53-55. These measurements were
performed according to the procedures described for 1 in Chapter 2. Crystallographic data
and details of the data collections and structure refinements are listed in Table 7.5 (for 50, 51,
and 53) and Table 7.6 (for 54 and 55).
7.6 References
1. (a) Jordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. (b) McKnight, A. L.; Waymouth, R. M.
Chem. Rev. 1998, 98, 2587.
2. Edelmann, F. T. Comprehensive Organometallic Chemistry III; Elsevier: Amsterdam, 2007, Vol. 4, p. 1.
3. (a) Piers, W. E.; Shapiro, P. J.; Bunel, E.; Bercaw, J. E. Syntlett. 1990, 74, 609. (b) Shapiro, P. J.;
Bunel, E.; Schaefer, W. P.; Bercaw, J. E. Orgnaometallics 1990, 9, 867. (c) Shapiro, P. J.; Cotter,
W. D.; Schaefer, W. P.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1994, 116, 4623. (d)
Hajela, S.; Bercaw, J. E. Orgnaometallics 1994, 13, 1147. (e) Voth, P.; Arndt, S.; Spaniol, T. P.;
Okuda, J. Organometallics 2003, 22, 65.
4. (a) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J. Organometallics 1999, 18, 2568. (b)
Ryu, J. –S.; Marks, T. J.; McDonald, F. E. Org. Lett. 2001, 3, 309. (c) Hong, S.; Kawaoka, A. M.;
Marks, T. J. J. Am. Chem. Soc. 2003, 125, 15878.
5. (a) Trifonov, A. A.; Spaniol, T. P.; Okuda, J. Organometallics 2001, 20, 4869. (b) Molander, G.
A.; Romero, J. A. G.; Corrette, C. P. J. Organomet. Chem. 2002, 647, 225. (c) Tardif, O.;
Nishiura, M; Hou, Z. Tetrahedron 2003, 59, 10525. (d) Robert, D.; Trifonov, A. A.; Voth, P.;
Okuda, J. J. Organomet. Chem. 2006, 691, 4393.
6. (a) Nishiura, M.; Hou, Z.; Wakatsuki, Y.; Yamaki, T.; Miyamoto, T. J. Am. Chem. Soc. 2003,
125, 1184. (b) Nishiura, M.; Hou, Z. J. Mol. Catal. A: Chem. 2004, 213, 101. (c) Liu, Y.;
Nishuira, M.; Wang, Y.; Hou, Z. J. Am. Chem. Soc. 2006, 128, 5592.
7. (a) Zhang, W.; Nishiura, M.; Hou, Z. J. Am. Chem. Soc. 2005, 127, 16788. (b) Zhang, W.;
Nishiura, M. Hou, Z. Synlett. 2006, 1213. (c) Zhang, W.; Nishiura, M.; Hou, Z.; Chem. Eur. J.
2007, 13, 4037. (d) Zhang, W.; Hou, Z. Org. Biomol. Chem. 2008, 6, 1720. (e) Zhang, W.;
Nishiura, M.; Mashiko, T.; Hou, Z.; Chem. Eur. J. 2008, 14, 2167.
8. Zhang, W.; Nishiura, M.; Hou, Z.; Angew. Chem., Int. Ed. 2008, 47, 9700.
9. Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973, 126.
10. Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics, 2006, 25, 3454.
Chapter 7
172
Table 7.5. Crystal Data and Collection Parameters of Complexes 50, 51, and 53.
compound 50 51 53.toluene
formula C21H49N4OScSi2 C21H49N4OSi2Y C30H59N4OSi2Y.C7H8
Fw 5474.78 518.72 729.04
cryst color, habit yellow, block colorless, needle colorless, platelet
cryst size (mm) 0.42 0.29 0.21 0.39 0.32 0.27 0.39 0.19 0.09
cryst syst monoclinic monoclinic triclinic
space group P21/n P21/n P-1
a (Å) 10.2069(9) 13.0811(9) 10.342(2)
b (Å) 45.951(4) 13.9981(10) 14.180(3)
c (Å) 12.2179(10) 15.5752(11) 14.488(3)
(deg) 80.338(3)
(deg) 104.3643(15) 94.0001(12) 88.135(3)
(deg) 77.763(3)
V (Å3) 5551.3(8) 2845.0(3) 2046.9(7)
Z 4 4 2
calc, g.cm-3 1.136 1.211 1.183
µ(Mo Kα), cm-1 3.69 21.52 15.14
F(000), electrons 2080 1112 784
θ range (deg) 2.45, 26.37 2.91, 27.10 2.47, 25.68
Index range (h, k, l) ±12, ±57, ±15 ±16, ±17, -19:18 ±12, ±17, -16:17
Min and max transm 0.8363, 0.9254 0.4221, 0.5594 0.5440, 0.8726
no. of reflns collected 43233 23107 15273
no. of reflns collected 11285 6171 7590
no. of reflns with F0 ≥ 4 σ (F0) 7141 4444 4882
wR(F2) 0.1356 0.0946 0.1419
R(F) 0.0617 0.0436 0.0606
weighting a, b 0.0564, 0 0.0459, 0 0.0649, 0
Goof 0.981 1.024 0.975
params refined 543 458 426
min, max resid dens -0.72, 0.94(9) -0.48, 0.88(9) -0.53, 0.68(10)
T (K) 100(1) 100(1) 100(1)
Rare Earth Organometallics with Dianionic Tetradentate Ligands Derived from the Me3DAPA moiety
173
Table 7.5. Crystal Data and Collection Parameters of Complexes 54, and 55.
compound 54 55
formula C25H47LaN4OSi C34H70LiN4OSi3Y
Fw 586.67 731.06
cryst color, habit yellow, block yellow, block
cryst size (mm) 0.35 0.29 0.15 0.56 0.43 0.39
cryst syst monoclinic monoclinic
space group P21/n P21/n
a (Å) 10.0158(6) 10.3454(12)
b (Å) 16.0585(9) 20.528(2)
c (Å) 18.2941(11) 21.153(2)
(deg)
(deg) 92.7492(9) 91.553(2)
(deg)
V (Å3) 2939.0(3) 4490.6(8)
Z 4 4
calc, g.cm-3 1.326 1.081
µ(Mo Kα), cm-1 15.16 14.05
F(000), electrons 1216 1576
θ range (deg) 2.54, 26.02 2.77, 26.02
Index range (h, k, l) ±12, -19:18, ±22 ±12, 0:25, 0:26
Min and max transm 0.5783, 0.7966 0.4098, 0.5463
no. of reflns collected 19202 8776
no. of reflns collected 5767 8776
no. of reflns with F0 ≥ 4 σ (F0) 4554 5578
wR(F2) 0.0849 0.1204
R(F) 0.0359 0.0495
weighting a, b 0.0401, 0.7319 0.0647, 0
Goof 1.038 0.925
params refined 297 415
min, max resid dens -0.35, 1.02(8) -0.37, 0.96(9)
T (K) 222(1) 100(1)
Chapter 7
174
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
175
Chapter 8 Organo Rare Earth Metal Complexes with a
Sterically Demanding Guanidinate Ligand
8.1 Introduction
Cationic organo rare earth metal chemistry is an area of vigorous research largely due to
the interesting catalytic capabilities exhibited by these species.1 Although a lot of effort has
been made to develop ancillary ligands that can support these catalytically active
species,1b,c,2 little is as yet known about ligand effects (steric as well as electronic) on their
performance. In recent years, our research group successfully developed the use of
sterically demanding amidinates [RC(NAr)2]- (Ar = 2,6-iPr2C6H3, R = Ph, C6F5, p-MeOPh)
as ligands for neutral and cationic organo rare earth metal catalysts for ethylene
polymerization and intramolecular hydroamination/cyclization of aminoalkenes.3 The
electron donating ability of this type of sterically demanding amidinate ligands can be
tuned by varying the group R on the NCN backbone, which can influence the
electrophilicity of the metal center.
Guanidinate anions [RNC(NR’2)NR”]-, closely related to the amidinates, have been
successfully applied in main group and transition metal chemistry.4 Nevertheless, their
application in organo rare earth metal chemistry has until now been limited to
bis(guanidinate) metal monoalkyl or -hydrido compounds and the chemistry of
mono(guanidinate) rare earth metal compounds has barely been investigated.5 Only very
recently the first examples of mono(guanidinate) dialkyl complexes of yttrium, using the
[(Me3Si)2NC(NR)2]- (R = Cy and iPr) ligands, were reported,6 but subsequent attempts to
generate the corresponding cationic yttrium alkyl species were not successful.6b The success
of the sterically demanding amidinate ligands in stabilizing such cationic rare earth metal
species prompted us to investigate the potentials of the sterically demanding guanidinate
ligand [Me2NC(NAr)2]- in this area. This should allow us to access catalysts that are
sterically similar to the related amidinate complexes, but less strongly electron deficient,
due to the possibility of the lone pair of the Me2N-group to interact with the conjugated
NCN ligand backbone.4
In this chapter, we describe the synthesis and characterization of neutral dialkyl and
cationic monoalkyl scandium, yttrium, and lanthanum complexes supported by the
sterically demanding guanidinate ligand [Me2NC(NAr)2]- (Ar = 2,6-iPr2C6H3) and a
comparative study of their performances in the catalytic hydroamination/cyclization of
aminoolefins and hydrosilylation of terminal alkenes. Catalytic data for the same
transformations by the amidinate yttrium complexes [RC(NAr)2]Y(CH2SiMe3)2(THF) (Ar =
Chapter 8
176
2,6-iPr2C6H3, R = Ph, C6F5, p-MeOPh) are included for comparison with the guanidinate
yttrium dialkyl complex to illustrate how the ancillary ligands affect the catalytic
performances of this family of catalysts.
8.2 Synthesis of a Sterically Demanding Guanidine
The guanidine employed in this chapter, ArNHC(NMe2)NAr (Ar = 2,6-iPr2C6H3, HL19),
was described previously in the patent literature as an insecticidal agent and was
synthesized by reaction of the carbodiimide ArN=C=NAr with dimethylamine under
forcing conditions.7 In this study, we synthesized this compound by hydrolysis of the
lithium guanidinate Li[Me2NC(NAr)2], which was prepared by reaction of LiNMe2 with 1
equiv of ArN=C=NAr in THF (Scheme 8.1). It was obtained as an off-white solid in a yield
of 85%. This guanidine ligand was characterized by NMR spectroscopy and elemental
analysis. The 1H NMR resonance of NH in C6D6 is found at δ 5.25 ppm.
Scheme 8.1. Synthesis of Guanidine ArNHC(NMe2)NAr HL19.
8.3 Synthesis of Neutral Organo Rare Earth Metal Complexes with the
Sterically Demanding Guanidine Ligand HL19
8.3.1 Synthesis of Scandium, Yttrium, and Lanthanum Dialkyl Complexes (L19)M(CH2SiMe3)2(THF)x
Reactions of the group 3 metal trialkyls M(CH2SiMe3)3(THF)2 (M = Sc and Y)8 with the
ligand precursor HL19 in toluene afforded complexes (L19)M(CH2SiMe3)2(THF) (M = Sc,
57; M = Y, 58) as colorless crystalline materials after recrystallization from a pentane
solution (isolated yields: 57, 82%; 58, 78%), as shown in Scheme 3.1. Since a related
lanthanum trialkyl complex La(CH2SiMe3)3(THF)x is not available, we followed the in situ
approach described before for TACN-amide and amidinate dialkyl complexes of
lanthanum.3b,9 In a one-pot procedure, LaBr3(THF)4 suspended in THF was reacted with 3
equiv of LiCH2SiMe3 at 0 ºC for 1 h, after which the ligand precursor HL19 was added. This
reaction afforded the lanthanum dialkyl complex (L19)La(CH2SiMe3)2(THF)2 (59) as a
yellow crystalline solid (isolated yield: 57%) after recrystallization from a pentane solution.
Room temperature 1H NMR spectra of these complexes in C6D6 suggest an (averaged) C2v
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
177
symmetry in solution, indicating fast rearrangement around the metal center on the NMR
time scale. The 1H NMR resonances of the M-CH2 groups are found at δ 0.12, -0.31 (d, JYH
= 2.9 Hz), and 0.56 ppm for 57, 58, and 59, respectively. The corresponding 13C NMR
resonances are found at δ 42.7 ppm (t, JCH = 105.7 Hz) for 57, δ 37.6 ppm (dt, JCH = 98.5
Hz, JYC = 38.9 Hz) for 58, and 54.9 ppm (t, JCH = 99.8 Hz) for 59. Complex 58 contains a
single coordinated THF molecule, while there are two in the related guanidinate yttrium
dialkyl complexes [(Me3Si)2NC(NR)2]Y(CH2SiMe3)2(THF)2 (R = Cy and iPr).6 This
indicates that the ligand [Me2NC(NAr)2]- (Ar = 2,6-iPr2C6H3) is the more sterically
demanding of the three. The scandium and yttrium dialkyl complexes 57 and 58 in C6D6 are
stable at ambient temperature for at least one day without noticeable decomposition. In
contrast, the lanthanum complex 59 in C6D6 is thermally labile under these conditions and
complete decomposition to ill-defined species was observed with release of 2 equiv of TMS
within 2h.
Scheme 8.2. Synthesis of Dialkyl Complexes 57-59.
Table 8.1. The 13C{1H} NMR Resonances of YCH2SiMe3 in C6D6 for 58 and 60a-60c.
complex δ / ppm JYC / Hz
58 37.6 38.9
60a 39.0 39.8
60b 39.5 40.3
60c 41.2 41.5
The guanidinate yttrium complex 58 was compared with the related amidinate complexes
[RC(NAr)2]Y(CH2SiMe3)2(THF) (Ar = 2,6-iPr2C6H3, R = p-MeOPh, 60a; R = Ph, 60; R =
C6F5, 60c).3 The 13C NMR resonances of YCH2 in these complexes are listed in Table 8.1
Chapter 8
178
and they are downfield shifted in the order of 58 < 60a < 60b < 60c, suggesting that the
electron donating ability of these four ligands decreases in order of [Me2NC(NAr)2]- >
[p-OMePhC(NAr)2]- > [PhC(NAr)2]
- > [C6F5C(NAr)2]-. The amidinate complex 60b can
bind an additional THF molecule to form the bis-THF adduct 60b(THF),3a whereas it is not
possible for the guanidinate complex 58 to form 58(THF) under the same conditions. This
indicates that the guanidinate ligand [Me2NC(NAr)2]- is more sterically demanding than the
benzamidinate ligand [PhC(NAr)2]- (also see the structural comparison of 58 and 60b
described below). The electronic and structural features of these complexes have significant
effects on their catalytic performances in the hydrosilylation reaction of terminal alkenes
and the intramolecular hydroamination/cyclization of aminoalkenes. This will be discussed
later in this chapter.
Figure 8.1. Structures of Complexes 57 (left), 58 (middle), and 59 (right). All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level.
Complexes 57-59 were characterized by single-crystal X-ray diffraction and their
structures are shown in Figure 8.1 (with the geometric data compiled in Table 8.2). In
overall geometry, they are similar to their amidinate congeners
[PhC(NAr)2]M(CH2SiMe3)2(THF)x (M = Sc, Y, and La).3b Here, only the comparison of
yttrium complexes 58 and 60b is given. The Y-C bond distances (2.388(2) Å and 2.407(2)
Å) in 58 are somewhat longer than those in 60b (2.374(4) Å and 2.384(4) Å). The angles
C(1)-N(1)-Y = 137.40(19)o and C(16)-N(2)-Y = 138.89(18)o in 58 are noticeably smaller
than the corresponding angles (C(8)-N(1)-Y = 144.25(19) Å, C(20)-N(2)-Y = 143.31(19) Å)
in 60b, indicating that the guanidinate L19 is more sterically demanding than the amidinate
ligand [PhC(Ar)2]-. There appears to be considerable interaction of the lone pair of Me2N
with the conjugated NCN moiety, as seen from the following structure features in 58:4 (i)
The three C-N distances in the guanidinate CN3 moiety are all very similar (C(13)-N(1) =
1.342(4) Å, C(13)-N(2) = 1.359(4) Å, C(13)-N(3) = 1.367(4) Å); (ii) The geometry around
N in the Me2N-group is essentially planar (the sum of angles around N3: 359.7(3)˚); (iii)
The dihedral angle formed by the planes C(14)-N(2)-C(15) and N(1)-C(13)-N(3) is only
27.3(4)˚. This interaction should make the yttrium center in 58 less electron deficient than
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
179
that in 60a, which is confirmed by NMR spectroscopy (see above). These features are also
present in the structures of scandium and lanthanum complexes 58 and 59. In the other
reported guanidinate dialkyl yttrium compounds [(Me3Si)2NC(NR)2]Y(CH2SiMe3)2(THF)2
(R = Cy and iPr),6 this delocalization can be ruled out by the R-N-C-N dihedral angles of
around 90o, and the corresponding elongation of the R2N-C bond by about 0.1 Å relative to
the other C-N bonds in the ligand.
Table 8.2. Selected Geometrical Data of Compounds 57, 58, and 59.
57 58 (M = Y) 59 (M = La)
Bond Distances (Å)
Sc(1)-N(11) 2.190(4) M-N(1) 2.345(2) 2.5341(17) Sc(1)-N(13) 2.205(4) M-N(3) 2.338(2) 2.5504(17)
Sc(1)-O(1) 2.212(3) M-O(1) 2.363(2) 2.6220(16) Sc(1)-C(128) 2.236(5) M-O(2) 2.6253(16)
Sc(1)-C(132) 2.240(5) M-C(28) 2.388(3) 2.578(2) C(113)-N(11) 1.340(6) M-C(32) 2.407(3) 2.576(2)
C(113)-N(12) 1.373(6) C(13)-N(1) 1.342(4) 1.348(3) C(113)-N(13) 1.349(6) C(13)-N(2) 1.359(4) 1.373(3)
C(13)-N(3) 1.367(4) 1.342(3) Bond Angle (deg)
C(11)-N(11)-Sc(1) 139.5(3) C(1)-N(1)-M 137.40(9) 131.99(13) C(116)-N(12)-Sc(1) 139.2(3) C(16)-N(2)-M 138.89(18) 134.97(14)
N(11)-Sc(1)-N(13) 61.27(14) N(1)-M-N(3) 57.47(8) 52.85(6) Sc(1)-C(128)-Si(11) 134.2(3) M-C(28)-Si(1) 119.80(16) 133.45(11)
Sc(1)-C(132)-Si(12) 122.2(3) M-C(32)-Si(2) 129.02(14) 143.65(11)
8.3.2 Synthesis of Lanthanum Dibenzyl Complex (L19)La(CH2Ph)2(THF)2
As mentioned above, the lanthanum dialkyl complex 59 is thermal labile at ambient
temperature and decomposes via TMS elimination. To make a thermally more robust
guanidinate organolanthanum complex, La(CH2Ph)3(THF)3 was used as an
organolanthanum starting material,10 since the possibility of multihapto bonding of the
benzyl group can impart additional thermal stability to organo rare earth metal complexes
with low coordination numbers.11 Reaction of La(CH2Ph)3(THF)3 with HL19 in THF
afforded the dibenzyl complex (L19)La(CH2Ph)2(THF) (61) as a yellow crystalline solid
after crystallization from a THF/n-hexane mixture in a yield of 72% (Scheme 8.3). The
reaction was seen to be quantitative in an NMR-tube scale reaction. This dibenzyl complex
is thermally stable in C6D6 for at least three days at ambient temperature without noticeable
Chapter 8
180
decomposition. The 1H NMR resonance (in C6D6) of LaCH2 is present at δ 2.24 ppm, with
the corresponding 13C NMR resonance at δ 68.7 ppm (JCH = 138.8 Hz). A crystal structure
determination of 61 (Figure 8.2, together with selected bond lengths and angles) shows that
the two benzyl groups are η2-bound to the lanthanum center with La-C-Cipso angles of
81.62(18)º and 91.4(2)º and La-Cipso distances of 2.810(3) Å and 2.999(3) Å. The related
amidinate lanthanum dibenzyl complex [PhC(NAr)2]La(CH2Ph)2(THF) contains one η2-
and one η3-bound benzyl group;10 this also indicates that the guanidinate ligand
[Me2NC(NAr)2]- (L19) is more sterically demanding than the amidinate ligand [PhC(NAr)2]
-
(Ar = 2,6-iPr2C6H3).
Scheme 8.3. Synthesis of Lanthanum Dibenzyl Complex 61.
Figure 8.2. Structure of Complex 61. All hydrogen atoms are omitted for clarity and thermal ellipsoids are drawn at the 50% probability level. Selected bond distances (Å)
and angles (deg): La-N(1) = 2.489(3), La-N(3) = 2.523(3), La-O = 2.543(2), La-C(28) = 2.630(3), La-C(29) = 2.810(3), La-C(35) = 2.596(3), La-C(36) = 2.999(3), La-C(28)-C(29) = 81.62(18), La-C(35)-C(36) = 91.4(2).
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
181
8.3.3 Synthesis of Bis(Guanidinate) Monobenzyl Complex (L19)2LaCH2Ph
For the sterically less demanding guanidate ligands [(Me3Si)2NC(NR)2]- (R = Cy and
iPr),6 bis(ligand) rare earth metal alkyl complexes have been reported. To see whether this is
possible for the sterically more demanding guanidinate L19, reaction of the dialkyl
complexes 57-59 and 61 with 1 more equiv of HL19 were performed on an NMR-tube scale.
For scandium and yttrium complexes 57 and 58, no further reactivity with HL19 was
observed. The lanthanum complexes 58 or 61 do react with HL19 to form
bis(guanidinate)La species with concomitant liberation of 1 equiv of TMS or toluene. On a
preparative scale, bis(guanidinate)lanthanum monobenzyl (L19)2LaCH2Ph (62) was
obtained (isolated yield: 64%) as a yellow crystalline solid by reaction of
La(CH2Ph)3(THF)3 with 2 equiv of HL19 in THF followed by recrystallization from a
toluene/n-hexane mixture (Scheme 8.4). The 1H NMR spectrum of 62 in toluene-d8 show
broad resonances, indicating fluxionality. However, raising the temperature to 80 ºC or
lowering the temperature to -60 ºC does not result in a well-resolved spectrum.
Scheme 8.4. Synthesis of Lanthanum Monobenzyl Complex 62.
The identity of (L19)2LaCH2Ph (62) was confirmed by a single-crystal X-ray study
(Figure 8.3, together with selected bond lengths and angles) on the isolated material. This
complex contains two monoanionic bidentate ligands L19 and a benzyl ligand which is
η3-bound to the lanthanum. One of the two ligands is coordinated to the metal more
symmetrically than the other, as seen by the difference of 0.07 Å between La-N(1) and
La-N(3) distances compared with that of 0.03 Å between La-N(4) and La-N(6) distances.
The η3-bound benzyl ligand contains a phenyl group that is significantly tilted with a
difference of 0.954 Å between the two La-Co distances.
Chapter 8
182
Figure 8.3. Structure of 62. All hydrogen atoms are omitted for clarity and thermal
ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and angles
(deg): La-N(1) = 2.579(2), La-N(3) = 2.509(2), La-N(4) = 2.532(2), La-N(6) = 2.499(3),
La-C(55) = 2.582(3), La-C(56) = 2.971(3), La-C(61) = 3.067(3), C(13)-N(1) = 1.342(4),
C(13)-N(2) = 1.359(4), C(13)-N(3) = 1.367(4), C(40)-N(4) = 1.354(3), C(40)-N(5) =
1.377(4), C(40)-N(6) = 1.342(3), La-C(55)-C(56) = 90.44(19).
8.4 Generation of Cationic Species from Neutral Complexes 57-59
Upon reaction with 1 equiv of [PhNMe2H][B(C6F5)4] in THF-d8, neutral complexes
57-59 are cleanly converted the corresponding cationic species
[(L19)M(CH2SiMe3)(THF-d8)x]+ (M = Sc, Y, or La) with concomitant release of TMS, as
seen by 1H NMR spectroscopy. The yttrium and lanthanum monoalkyl cations were isolated
(from reactions using the [PhNMe2H][B(C6H5)4] reagent) as their tetraphenylborate salts
[(L19)M(CH2SiMe3)(THF)x]+[B(C6H5)4]
- (M = Y, x = 3, 63; M = La, x = 4, 64) as colorless
crystalline solids after crystallization from THF/cyclohexane. Complexes 63 and 64 contain
three and four THF molecules per metal, respectively, as seen by elemental analysis. The 1H
NMR resonances of MCH2 in THF-d8 are found at δ -0.40 ppm (d, JYH = 3.2 Hz) for 63 and
δ -0.18 ppm for 64, with the corresponding 13C NMR resonances present at δ 39.7 ppm (dt,
JYC = 44.5 Hz, JCH = 96.4 Hz) and δ 66.0 ppm (t, JCH = 99.2 Hz).
The structure of complex 63 (Figure 8.4, with selected bond lengths and angles) reveals a
cation with a 6-coordinated yttrium center; the coordination sphere is composed of two
nitrogen atoms of the guanidinate ligand L19, one trimethylsilylmethyl group, and three
THF molecules. The ligand L19 binds to the yttrium center more asymmetrically than that in
its neutral precursor 58, as seen by the larger difference between the two Y-N bond
distances in 63 than that in 58 (0.048 Å for 63; 0.007 Å for 58). Conversion of the neutral
complex 58 to the cationic complex 63 increases the coordination number of yttrium from 5
to 6, which might explain the small change in the average Y-N bond distance (2.3438(19) Å
for 73 and 2.342(2) Å for 58) in this process. The Y-C bond distance of 2.369(2) Å in 63 is
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
183
noticeably shorter than the average Y-C distance (of 2.398(3) Å) in 58, indicating a more
electrophilic yttrium center in the cation of 63.
Figure 8.4. Structure of 63. All hydrogen atoms and the tetraphenylborate anion are omitted for clarity; Thermal ellipsoids are drawn at the 50% probability level. Selected
bond lengths (Å) and angles (deg): Y(1)-O(1) = 2.3783(14), Y(1)-O(2) = 2.4029(14), Y(1)-O(3) = 2.3714(14), Y(1)-N(11) = 2.3676(18), Y(1)-N(13) = 2.3200(18), Y(1)-C(128) = 2.369(2), Y(1)-C(128)-Si(1) = 148.85(12).
8.5 Comparative Catalysis Study of Neutral and Cationic Complexes
with Sterically Demanding Amidinate and Guanidinate Ligands
8.5.1 Catalytic Hydrosilylation of Terminal Alkenes
Metal-catalyzed hydrosilylation of alkenes is the most straightforward and
atom-economic way to synthesize organosilanes. These can be converted to the
corresponding alcohols by oxidation,12 or used as monomers for the production of
silicon-based polymers, applied as rubbers, paper release coatings, and pressure-sensitive
adhesives.13 Pt-based catalysts are known to catalyze hydrosilylation with very high
efficiency,14 but when RSiH3 is employed as silylating reagent, they tend to form mixtures
of reduced olefin R’H, RR’SiH2, RR’2SiH, and RR’3Si.14a Catalysts based on early
transition metals,15 actinides,16 and rare earth metals17 have been reported to show good
selectivity for PhRSiH2 in the hydrosilylation of olefins with PhSiH3. Nevertheless, the low
turnover frequency of these catalysts limits their application in synthesis. To date, the most
efficient catalyst from this family is Me2SiCp”2SmCH(SiMe3)2 (tof = 120 h-1 at room
temperature for 1-hexene), remarkably with a high selectivity for the Markovnikov product
(76 %).17c [Me2Si(C5Me4)(μ-PCy)LuCH2SiMe3]2 has been reported to catalyze the
hydrosilylation of 1-hexene with a similar efficiency and full selectivity for the
anti-Markovnikov product, when a 25 % excess of PhSiH3 and 5 mol% catalyst are used.17j
Here we perform a comparative study of the catalytic hydrosilylation reaction of terminal
alkenes catalyzed by neutral dialkyl complexes described in this chapter and the
Chapter 8
184
(mono)amidinate yttrium dialkyl complex [RC(NAr)2]Y(CH2SiMe3)2(THF) (60a-60c),
attempting to illustrate how the ancillary ligands and the ionic radius affect the catalytic
performances.
Firstly, to see how the ancillary ligands affect the catalyst performances, the
mono(guanidinate) and mono(amidinate) yttrium dialkyl complexes (58 and 60a-60c) are
tested for the alkene hydrosilylation reaction using PhSiH3 in small (4%) excess. A range of
terminal alkenes were used as substrates and the results are summarized in Table 8.3. For
all the substrates (65a-65i), the reaction went essentially to completion and Lewis basic
acetal or 1,3-dithiane groups pose no problems. No side reactions (such as olefin
hydrogenation, dimerization of alkenes, and dehydrogenative coupling of organosilanes,
that are known to occur with rare-earth metal or actinide catalysts16,17h) were observed for
catalysts 58 and 60a-60c. Full selectivity for anti-Markovnikov products was obtained
when unfunctionalized olefins were employed as substrates (entry 1-5). For the sterically
demanding substrate 3,3-dimethylbut-1-ene (65e, entry 5), the least electron deficient
amidinate complex 60a is noticeably the most active catalyst among the three amidinate
catalysts (with similar sterics around the yttrium center). However, for the guanidinate
complex 58, the efficiency gained from the increased electron donating ability of the ligand
is offset by the increased steric hindrance around the metal center. For the less sterically
demanding alkene with a 1,3-dithiane functionality (65f, entry 6), the catalyst activity is
predominantly controlled by the electronic property of the catalyst; as such, the least
electron deficient catalyst, the guanidinate complex 58, is clearly the most efficient and the
most electron deficient amidinate catalyst 60c is the least effective. 4,4-Diethoxybut-1-ene
(65h) is remarkably rapidly hydrosilylated, but now yields predominantly the Markovnikov
product (entry 8), and differences between 58 and 60b are visible both in activity and
selectivity. The guanidinate catalyst 58 is clearly faster, but yields a 3:1 M:AM isomer
mixture, whereas 60b has a 93% selectivity for the branched (M) product. As the olefin in
substrate 65h is not expected to have an electronic preference for 2,1-insertion into an Y-H
species (metal hydrides are the proposed active species in rare-earth metal catalyzed
hydrosilylation17h,k,18), the preference for the branched (Markovnikov) product is likely to
stem from interaction of the substrate ether groups with the metal center. The most stable
chelate (with intramolecular Y-O coordination), resulting from insertion of the olefin into
the Y-H bond, is likely to be the 5-membered chelate (from 2,1-insertion) rather than the
6-membered chelate (from 1,2-insertion). It could also be possible that ether coordination
precedes olefin insertion, in which case the geometry for 2,1-insertion is likely to be the
most favorable. Although we did not succeed in observing organometallic intermediates in
the reactions, it can be expected that an increased affinity of the metal for the ether function
will lead to an increased selectivity for the branched product 66h. This would lead to the
conclusion that the metal center in the guanidinate catalyst 58 is less electrophilic than that
in the amidinate catalyst 60b, which is consistent with the structural and spectroscopic
observations made above. Styrene requires a higher temperature (80 ˚C) to give conversion,
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
185
and then yields the benzylic silane 67g as main product (entry 9). That styrene
hydrosilylation is more sluggish may be due to η3 coordination of the 1-phenylethyl group
formed by 2,1-insertion of styrene into a Y-H species. An yttrium η3-1-phenylethyl complex
was reported from the reaction of styrene with [Y(η5:η1-C5Me4SiMe2NtBu)(THF)(μ-H)]2.
19
Internal olefins (e.g. cis-4-octene and cyclohexene) are not converted under the applied
conditions.
Table 8.3. Catalytic Hydrosilylation of Terminal Alkenes by the Guanidinate Yttrium
Catalyst 58 and the Amidinate Complexes 60a-60c.a
product selec. (%)b entry (Substrate)
R catalyst time (min)
olefin conv. (%)b 66 67
58 <5 100 >99 1(65a) 60b <5 100 >99
58 <5 100 >99 2(65b)
60b <5 100 >99
58 <5 100 >99 3(65c)
60b <5 100 >99
58 <5 100 >99 4(65d)
60b <5 100 >99
58 300 98 >99
60a <5 100 >99
60b 60 100 >99 5(65e)
60c 600 35 >99
58 <5 100 >99
60a 70 100 >99
60b 90 100 >99 6(65f)
60c 600 65 >99
58 240 98 96 4 7(65g)
60b 720 98 96 4
58 25 100 26 74 8(65h)
60b 90 100 7 93
58 70 100 33 67 9(65i)c
60b 100 100 23 77 a Reaction conditions: catalyst: 58 or 60a-60c (10μmol), olefin (0.5 mmol), PhSiH3 (0.52
mmol), 23˚C, solvent: C6D6 (0.3 ml). b Determined by GC-MS and in situ 1H NMR
spectroscopy. c 80˚C.
Chapter 8
186
Table 8.4. Catalytic Hydrosilylation of Terminal Alkenes by Mono(guanidinate) Scandium,
Yttrium, and Lanthanum Complexes 57-59.
product selec.
(%)b
entry
(Substrate)
substrate catalyst time
(min)
olefin
conv. (%)b
66 67
57 75c 100 >99
58 <5 100 >99 1(65a) 59 <5 100 89 11
58 <5 100 >99 2(65c)
59 <5 100 92 8
58 <5 100 >99 3(65d)
59 <5 100 91 9
58 300 98 >99 4(65e)
59 180 98 96 4
57 960c 76 >99
58 <5 100 >99 5(65f) 59 <5 100 89 11
58 240 98 96 4 6(65g)
59 15 100 71 29
58 25 100 26 74 7(65h)
59 10 100 53 47
58 70d 100 33 67 8(65i)
59 30 100 23 77 a Reaction conditions: catalyst: 57-59 (10μmol), olefin (0.5 mmol), PhSiH3 (0.52 mmol),
23˚C, solvent: C6D6 (0.3 ml). b Determined by GC-MS and in situ 1H NMR spectroscopy. c
50 ˚C. d 80 ˚C.
Secondly, to see how the metal ionic radius affects the catalyst performances, the
mono(guanidinate) scandium, yttrium, and lanthanum dialkyl complexes 57-59 are tested
for the hydrosilylation reactions of terminal alkenes and the results are listed in Table 8.4.
Compared with the yttrium and lanthanum complex 58 and 59, the scandium compound 57
show the lowest activity (entry 1 and 5) and conversion was observed only at higher
temperature (50 ºC), but full selectivity to anti-Markovnikov products was obtained. For
scandium catalyst 57, the sulfur-containing substrate (65f) slows the catalysis dramatically
compared with unfunctionalized alkenes (65a) (entry 1 and 5). For the sterically demanding
alkenes (65e and 65g, entry 6 and 7), 59 (lanthanum) shows noticeably higher activity than
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
187
58 (yttrium), which might be due to the large radius of lanthanum in 59. For all substrates
(except for 65h), the lanthanum catalyst shows increased selectivity for Markovnikov
products compared with the yttrium catalysts. Remarkably, styrene is rapidly hydrosilylated
at ambient temperature by the lanthanum catalyst 59 (entry 8), even though the formation of
a η3-1-phenylethyl complex for lanthanum should be more facile than for yttrium due to the
larger radius of lanthanum. Apparently, the larger size of the metal increases the kinetic
lability of this species for lanthanum relative to yttrium.
8.5.2 Catalytic Intramolecular Hydroamination/cyclization of Aminoalkenes
Another reaction that can be effectively catalyzed by organolanthanide catalysts is the
intramolecular hydroamination/cyclization of aminoalkenes.20 This reaction offers a
straightforward and atom-economical method to synthesize nitrogen-containing
heterocycles that are important for fine chemicals and pharmaceuticals. Here, we used
yttrium complexes bearing guanidinate and different amidinate ligands to illustrate ligand
effects for this reaction; and then we compared the catalytic performances of the neutral
and cationic rare earth organometallics described here in the hydroamination/cyclization of
N-methylpent-4-en-1-amine (S2) and 2,2-dimethylpent-4-en-1-amine (S3). All cationic
species are generated in-situ from the corresponding neutral precursors by reaction with
[PhNMe2H][B(C6F5)4].
Table 8.5. [RC(NAr)2]Y(CH2SiMe3)2(THF) catalyzed Hydroamination/cyclization of S2.a
entry Cat time / (min) conv. (%)b k (s-1)b
1 Me2N 110 >99 7.44 10-3 2 p-MeOPh 70 >99 1.15 10-2 3 Ph 65 >99 1.25 10-2 4 C6F5 240 >99 3.29 10-3
a conditions: catalyst (10 μmol), substrate (1 mmol), solvent: C6D6 (total volume: 0.5 mL),
temperature: 80 ºC; b Determined by in situ 1H NMR spectroscopy.
To see how the ancillary ligands affect the catalyst performances for this reaction, we
have compared the hydroamination/cyclization of S2 catalyzed by the mono(guanidinate)
and mono(amidinate) yttrium dialkyl complexes [RC(NAr)2]Y(CH2SiMe3)2(THF) (R =
Me2N, p-MeOPh, Ph, and C6F5) and the results are compiled in Table 8.5. All these four
yttrium catalysts show a zero-order dependence on substrate concentration over the full
conversion. For the yttrium catalysts by amidinate ligands with similar steric hindrance
Chapter 8
188
(entry 2-4), the most electron deficient catalyst with the electron withdrawing group C6F5
on the amidinate backbone shows the lowest activity (entry 4). In contrast, the most
electron rich catalyst with the guanidinate ligand L19 (entry 1) is not the most effective
catalyst, which might be due to the greater steric demand of the guanidinate ligand relative
to the amidinate ligands. Thus, it appears that a good hydroamination/cyclization catalyst
(with amidinate or guanidinate ligands) combines a relatively electron rich metal center and
a less sterically demanding ligand. In Chapter 3 we already noticed that the catalytic
conversion of the secondary amine substrate S2 is very sensitive to steric hindrance around
the metal center.
Table 8.6. Catalytic Hydroamination/Cyclization of S2 and S3.a
substrate entry catalyst time / (min) conv. (%)b k (s-1)b
1 57 450 >90 3.19 10-3 2 57/B 150c >99 6.53 10-3 3 58 35 >99 2.57 10-2 4 58/B 55c >99 1.96 10-2 5 59 35 >99 3.40 10-2 6 59/B 100c >99 9.50 10-3
7 57 60 0
8 57/B 60 0 9 58 380 >99 2.20 10-3
10 58/B 105 >99 7.88 10-3 11 59 25 >99 3.93 10-2 12 59/B 450 <30 nd
a conditions: catalyst (10 μmol), activator [PhNMe2H][B(C6F5)4] (B), where appropriate,
substrate (0.5 mmol), solvent: C6D6 (total volume: 0.5 mL), temperature: 60 ºC; b
Determined by in situ 1H NMR spectroscopy. c 80 ºC
To see how the metal ionic radius and the use of neutral versus cationic species affect the
catalytic performances, neutral dialkyl and cationic monoalkyl complexes of scandium,
yttrium, and lanthanum bearing the guanidinate ligand L19 are used as catalysts to study the
hydroamination/cyclization of S2 and S3 and the results are compiled in Table 8.6. For each
substrate, the catalyst with larger metal radius shows higher activity (entry 1, 3, and 5 for
S3; entry 7, 9, and 11 for S2). For primary amine S3, the neutral catalyst is significantly
more active than the corresponding cationic catalyst (e.g. entry 3 and 4; entry 5 and 6). For
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
189
secondary amine S2, no activity is observed for the scandium catalysts (both neutral and
cationic systems, entry 7 and 8); the cationic yttrium catalyst is more active than its neutral
precursor (entry 9 and 10); in contrast, the cationic lanthanum catalyst is less active than its
neutral precursor (entry 11 and 12). For both substrates, the neutral lanthanum complex is
the most effective catalyst in the entire series (entry 5 for S3 and entry 11 for S2).
The kinetics of all the effective catalysts (entry 1-6 and entry 9-11) were followed by in
situ NMR spectroscopy and all the reactions shows zero-order dependence in substrate
concentration over almost the full conversion range (characteristic of rate-limiting
intramoleculare alkene insertion to the metal-amido bond;20a-c Scheme 3.5). Plots of
substrate concentration versus time of the neutral lanthanum (for S2 and S3) are shown in
Figure 8.5. It is clear that for the secondary amine S2 it is linear over the full conversion,
but for the primary amine S3, it deviates from linearity for the last 20% conversion, which
might be due to the substrate inhibition depicted in Scheme 8.5.20b,c,e,f Such product
inhibition is not possible for the hydroamination product (tertiary amine) of the secondary
aminoalkenes.
R2 = 0.9992R2 = 0.9976
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30
Time / min
[Su
bs
tra
te]
/ M
3 + primary amine S3
3 + secondary amine S2
Figure 8.5. Plots of substrate concentration versus time for lanthanum dibenzyl complex 59
catalyzed hydroamination/cyclication of S2 and S3.
Scheme 8.5. Possible Product Inhibition Pathways for the Hydroamination/Cyclization of
Primary Aminoalkene.
Chapter 8
190
8.6 Concluding Remarks
We have shown that the sterically demanding guianidinate L19 is suitable to support
well-defined neutral dialkyl and cationic monoalkyl scandium, yttrium, and lanthanum
complexes and can thus be applied over the full size range of the rare earth metals. The
ionic radius of rare earth metal has a pronounced influence on the thermal stability of the
derived neutral dialkyl complexes, e.g. the lanthanum dialkyl complex 59 (with the largest
rare earth metal) decomposes within 2 h, whereas the complexes 57 and 58 bearing a
relatively smaller metal center scandium and yttrium are thermally stable. The stability of
the organolanthanum complex can be enhanced by changing the trimethylsilylmethyl group
by the benzyl group, which has a possibility to bind to the lanthanum in a multihapto mode,
as seen by the two η2-bound benzyl groups in 60.
The synthesized guanidinate complexes and the related amidinate complexes catalyze the
hydrosilylation of terminal alkenes and intramolecular hydroamination/cyclization of
aminoalkenes. Both the ancillary ligands and the ionic radius of catalysts have influences
on their catalyst performances. For the hydrosilylation reaction, the more electron donating
ability of the guanidinate ligand makes the guanidinate catalysts more effective toward
heteroatom-containing substrates than the amidinate catalysts, and this is likely due to the
relatively weak interaction between the heteroatom in the substrate and the less electron
deficient metal center in the guanidinate catalyst. For the sterically demanding substrates,
the steric effect of the catalysts appears to be substantially larger than their electronic effect
and the more sterically demanding guanidinate catalyst is less active than the amidinate
catalysts. Additionally, the catalysts with larger rare earth metals are more effective than
those with smaller metals, but above a certain size this is accompanied by a decreased
selectivity towards anti-Markovnikov products. Overall, these catalysts are extremely
efficient in the hydrosilylation of 1-alkenes, with particularly the Y-catalysts forming
anti-Markovnikov products selectively at rates of at least 600 t.o./h, with proven t.o.n.’s of
at least 50. This makes them by far the most effective rare-earth metal based hydrosililation
catalysts reported.
The ligand effects observed for the hydroamination/cyclization reaction with this type of
catalysts are similar, in the sense that the most effective catalysts have the most
electron-donating ligand, when steric effects are not important. Nevertheless, especially for
the secondary amine substrate S2, steric effects play a large role: the largest available metal
generally provides the best catalyst platform for this transformation.
It thus seems that the family of amidinate/guanidinate ligands provides a potentially
useful and flexible ancillary ligand set for rare-earth metal catalysts. In particular, a
judicious reduction of the steric hindrance of the substituents on the N-atoms of the NCN
backbone for the guanidinate might lead to some highly interesting catalysts, e.g. for the
hydosilylation of sterically hindered olefinic substrates.
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
191
8.7 Experimental Section
General Remarks. See the corresponding section in Chapter 2. GC-MS measurements
were performed on a HP 6890 series GC-system coupled with a HP 5973 mass selective
detector. Column: HP-5MS 5% phenyl methyl siloxane 30 m × 250 μm capillary column.
Temperature profile: start at 35 ˚C (hold for 10 min), then increasing to 280 ˚C at 20 ˚C/min,
and then hold at 280 ˚C for 10 min. The olefins 1-hexene, 1-octene, vinylcyclohexane,
4-vinyl-1-cyclohexene, 3,3-dimethyl-1-butene were commercial samples stirred at least 4 h
over Na/K alloy and then distilled under nitrogen. Styrene was dried over molecular sieves
and distilled before use. Bis(2,6-diisopropylphenyl)carbodiimide (TCI Europe Organic
Chemicals, >98%) and Phenylsilane (Aldrich, 99%, saturated with nitrogen) are used as
purchased. 2-(3’-Butenyl)-2-methyl-1,3-dithiane,23 2-(4’-pentenyl)-2-methyl-1,3-dithiane,23
4,4-Diethoxylbut-1-ene,24 M(CH2SiMe3)3(THF)2 (M = Sc and Y),9 La(CH2Ph)3(THF)3,10
N-methylpent-4-en-1-amine,25 and 2,2-dimethylpent-4-en-1-amine26 were prepared
according to literature procedures.
Synthesis of (L19)Sc(CH2SiMe3)2(THF) (57). To a solution of Sc(CH2SiMe3)3(THF)2
(219 mg, 0.486 mmol) in toluene (20 ml), was added a solution of HL19 (198 mg, 0.486
mmol) in toluene (5 ml). The resulting solution was stirred for 20 min at room temperature.
Then volatiles were removed under reduced pressure and the residue was dissolved in
pentane (4 ml). Upon standing at -30 ˚C overnight, crystalline material formed (including
crystals suitable for X-ray analysis). The mother liquor was decanted and the solid was
dried under vacuum, yielding the title compound (277 mg, 0.397 mmol, 82%) as an
off-white solid. 1H NMR (400 MHz, C6D6, δ): 7.10 (m, 6H, m-H, p-H-Ph), 3.73 (m, 4H,
α-H-THF), 3.63 (hept, 4H, JHH = 6.75 Hz, CH-iPr), 2.02 (s, 6H, NCH3), 1.04 (d, 12H, JHH =
6.74 Hz, CH3-iPr), 1.21 (d, 12H, JHH = 6.80 Hz, CH3-iPr), 1.19 (m, 4H, β-H-THF), 0.22 (s,
18H, Si(CH3)3), 0.12 (br, 4H, ScCH2). 13C NMR (100.6 MHz, C6D6, δ): 166.9 (s, NCN),
143.9 (s, ipso-C-Ph), 142.7 (s, o-C-Ph), 124.5 (d, JCH = 159.3 Hz, p-C-Ph), 124.2 (d, JCH =
153.6 Hz, m-C-Ph), 71.3 (t, JCH = 151.2 Hz, α-C-THF), 42.7 (t, JCH = 105.7 Hz, ScCH2),
40.0 (q, JCH = 136.0 Hz, NCH3), 28.0 (d, JCH = 127.6 Hz, CH-iPr), 25.7 (q, JCH = 125.7 Hz,
CH3-iPr), 25.1 (t, JCH = 135.0 Hz, β-C-THF), 24.1 (q, JCH = 125.7 Hz, CH3-iPr), 4.0 (q, JCH
= 116.4 Hz, Si(CH3)3). Anal. Calc for C39H70N3OScSi2: C, 67.10; H, 10.11; N, 6.02. Found:
C, 67.14; H, 10.18; N, 5.95.
Synthesis of (L19)Y(CH2SiMe3)2(THF) (58). This reaction was done by following the
procedure described for (L19)Sc(CH2SiMe3)2(THF). Y(CH2SiMe3)3(THF)2 (268 mg, 0.541
mmol) and HL19 (221 mg, 0.541 mmol) were used as reactants. The same workup
procedure yielded the title compound (316 mg, 0.415 mmol, 78%) as a colorless solid. 1H
NMR (400 MHz, C6D6, δ): 7.08 (m, 6H, m-H, p-H-Ph), 3.61 (hept, 4H, JHH = 6.67 Hz,
CH-iPr), 3.56 (m, 4H, α-H-THF), 2.01 (s, 6H, NCH3), 1.40 (d, 12H, JHH = 6.97 Hz,
CH3-iPr), 1.23 (d, 12H, JHH = 6.97 Hz, CH3-iPr), 1.12 (m, 4H, β-H-THF), 0.26 (s, 18H,
Si(CH3)3), -0.31 (d, 4H, JHH = 2.9 Hz, YCH2). 13C NMR (100.6 MHz, C6D6, δ): 166.7 (s,
Chapter 8
192
NCN), 144.0 (s, ipso-C-Ph), 142.4 (s, o-C-Ph), 124.0 (d, JCH = 156.3 Hz, m-C-Ph), 123.9 (d,
JCH = 159.1 Hz, p-C-Ph), 70.5 (t, JCH = 150.2 Hz, α-C-THF), 39.6 (q, JCH = 138.1 Hz,
NCH3), 37.6 (dt, JYC = 38.9 Hz, JCH = 98.5, YCH2), 28.1 (d, JCH = 127.7 Hz, CH-iPr), 25.9
(q, JCH = 123.8 Hz, CH3-iPr), 24.9 (t, JCH = 133.6 Hz, β-C-THF), 23.8 (q, JCH = 125.6 Hz,
CH3-iPr), 4.4 (q, JCH = 115.6 Hz, Si(CH3)3). Anal. Calc for C39H70N3OSi2Y: C, 63.12; H,
9.51; N, 5.66. Found: C, 62.95; H, 9.56; N, 5.55.
Synthesis of (L19)La(CH2SiMe3)2(THF)2 (59). To a suspension of LaBr3(THF)4 (2.00 g,
3.00 mmol) in THF (100 ml), was added a solution of LiCH2SiMe3 (0.847 g, 9.00 mmol) in
THF (10 ml) and the resulting mixture was stirred for 1 h at room temperature. Then a
solution of HL19 (1.22 g, 3.0 mmol) in THF (10 ml) was added and the mixture was stirred
for another 1 h at room temperature. All the volatiles were removed under vacuum and the
residual THF was stipped by stirring with pentane (5 × 10 ml) and subsequently pumping
off under vacuum. The residue was extracted with pentane (100 ml) and the extract was
then concentrated to 20 ml. Upon standing at - 30 ˚C overnight, crystalline material formed
(including crystals suitable for X-ray analysis). The mother liquor was decanted and the
solid was dried under vacuum yielding the title compound (1.47 g, 1.70 mmol, 57%) as an
off-white solid. 1H NMR (400 MHz, C7D8, δ): 7.06 (d, 4H, JHH = 7.43 Hz, m-H-Ph),
6.98(dd, JHH = 8.42 Hz, JHH = 6.65 Hz, p-H-Ph), 3.59 (hept, 4H, JHH = 6.79 Hz, CH-iPr),
3.57 (m, 4H, α-H-THF), 2.03 (s, 6H, NCH3), 1.38 (m, 4H, β-H-THF), 1.37 (d, 12H, JHH =
6.86 Hz, CH3-iPr), 1.23 (d, 12H, JHH = 6.86 Hz, CH3-iPr), 0.20 (s, 18H, Si(CH3)3), -0.56 (br,
4H, LaCH2). 13C NMR (100.6 MHz, C6D6, δ): 164.4 (s, NCN), 145.0 (s, ipso-C-Ph), 142.1
(s, o-C-Ph), 123.9 (d, JCH = 154.3 Hz, m-C-Ph), 123.3 (d, JCH = 158.7 Hz, p-C-Ph), 69.2 (t,
JCH = 148.0 Hz, α-C-THF), 54.9 (t, JCH = 99.8 Hz, LaCH2), 39.5 (q, JCH = 137.8 Hz, NCH3),
28.1 (d, JCH = 129.2 Hz, CH-iPr), 25.8 (q, JCH = 125.7 Hz, CH3-iPr), 25.3 (t, JCH = 132.3 Hz,
β-C-THF), 23.8 (q, JCH = 125.7 Hz, CH3-iPr), 4.7 (q, JCH = 115.8 Hz, Si(CH3)3). Anal. Calc
for C43H78LaN3O2Si2: C, 59.76; H, 9.10; N, 4.86. Found: C, 59.62; H, 9.11; N, 4.93.
Synthesis of (L19)La(CH2Ph)2(THF) (60). To a suspension of La(CH2Ph)3(THF)3 (311
mg, 0.495 mmol) in toluene (10 ml), was added a solution of HL19 (202 mg, 0.495 mmol)
in toluene (5 ml). The resulting solution was stirred for 10 min at room temperature. Then
the volatiles were removed under reduced pressure. The residue was suspended in pentane
(3 ml) and toluene (about 1 ml) was added to make a clear solution. Upon standing at -30
˚C overnight, crystalline material formed (including crystals suitable for X-ray analysis).
The mother liquor was decanted and the solid was dried under vacuum, yielding the title
compound (277 mg, 0.397 mmol, 82%) as a yellow solid. 1H NMR (400 MHz, C7D8, δ):
7.12 (d, 4H, JHH = 7.28 Hz, m-H-Ph), 7.04(dd, 2H JHH = 8.29 Hz, JHH = 6.72 Hz, p-H-Ph),
6.93 (t, 4H, JHH = 7.51 Hz, m-H-Ph), 6.45 (d, 4H, JHH = 7.45 Hz, o-H-Ph), 6.38 (t, 2H, JHH
= 7.18 Hz, p-H-Ph), 3.65 (septet, 4H, JHH = 6.79 Hz, CH-iPr), 2.71 (m, 4H, α-H-THF), 2.24
(s, 4H, LaCH2), 2.09 (s, 6H, NCH3), 1.35 (d, 12H, JHH = 6.88 Hz, CH3-iPr), 1.27 (d, 12H,
JHH = 6.88 Hz, CH3-iPr), 1.00 (m, 4H, β-H-THF). 13C NMR (100.6 MHz, C6D6, δ): 165.8 (s,
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
193
NCN), 150.1 (s, ipso-C-Ph), 145.2 (s, ipso-C-Ph), 141.7 (s, o-C-Ph), 131.7 (d, JCH = 154.2
Hz, o-C-Ph), 123.9 (d, JCH = 154.2 Hz, m-C-Ph), 123.3 (d, JCH = 158.2 Hz, p-C-Ph), 120.9
(d, JCH = 154.2Hz, m-C-Ph), 115.7 (d, JCH = 160.1 Hz, p-C-Ph), 68.9 (t, JCH = 147.6 Hz,
α-C-THF), 68.7 (t, JCH = 138.8 Hz, LaCH2), 39.6 (q, JCH = 137.8 Hz, NCH3), 28.3 (d, JCH =
126.8 Hz, CH-iPr), 25.8 (q, JCH = 125.5 Hz, CH3-iPr), 25.4 (t, JCH = 134.3 Hz, β-C-THF),
23.9 (q, JCH = 125.5 Hz, CH3-iPr). Anal. Calc for C45H62LaN3O: C, 67.57; H, 7.81; N, 5.25.
Found: C, 67.66; H, 7.84; N, 5.10.
Synthesis of (L19)2LaCH2Ph (61). To a suspension of La(CH2Ph)3(THF)3 (320.6 mg,
0.51 mmol) in THF (15 mL) was added a solution of HL19 (415.0 mg, 1.02 mmol) in THF
(5 mL) and the mixture was stirred for 6 h at 50 ºC. All the volatiles were removed under
reduced pressure and the residue was purified by recrystallization from a toluene/n-hexane
solution, yielding the title compound (340.5, 0.33 mmol, 64%) as a yellow crystalline solid.
The NMR spectra of this compound show broad resonances. Anal. Calc. for C61H87LaN6: C,
70.23; H, 8.41; N, 8.06. Found: C 69.35; H, 8.42; N, 7.80.
In situ Generation of [(L19)Sc(CH2SiMe3)(THF-d8)x][B(C6H5)4]. THF-d8 (0.5 mL)
was added to a mixture of 57 (43.2 mg, 50 μmol) and [PhNMe2H][B(C6H5)4] (22.1 mg, 50
50 μmol ) and the resulting suspension was homogenized by agitation. The solution was
transferred to an NMR tube equipped with a Teflon Young valve and analyzed by NMR
spectroscopy, which indicated the clean formation of the title compound with release of 1
equiv of TMS and free PhNMe2. 1H NMR (400 MHz, THF-d8) δ: 7.27 (br, 8H, o-H-PhB),
7.23 (d, 4H, JHH = 7.23 Hz, m-H PhN), 7.19 (t, 2H, JHH = 6.72 Hz, p-H PhN), 6.84 (t, 8H,
JHH = 7.28 Hz, m-H-PhB), 6.70 (t, 4H, JHH = 7.04 Hz, p-H-PhB), 3.26 (septet, 4H, JHH =
6.61 Hz, CH-iPr), 2.26 (s, 6H, NCH3), 1.28 (d, 12H, JHH = 6.60 Hz, CH3-iPr), 1.24 (d, 12H,
JHH = 6.60 Hz, CH3-iPr), 0.49 (s, 2H, ScCH2), 0.01 (s, 9H, Si(CH3)3). 13C{1H} NMR (100.6
MHz, THF-d8) δ: 169.3 (NCN), 166.4 (q, JBC = 48.4 Hz, ipso-C PhB), 144.0 (o-C PhN),
143.5 (ipso-C PhN), 138.3 (o-C PhB), 127.6 (p-C PhN), 126.9 (m-C PhB), 126.6 (m-C
PhN), 123.0 (p-C PhB), 55.5 (ScCH2), 41.8 (NCH3), 30.3 (CH-iPr), 26.9 (CH3-iPr), 25.3
(CH3-iPr), 4.5 (Si(CH3)3).
Synthesis of [(L19)Y(CH2SiMe3)(THF)3][B(C6H5)4] (63). THF (0.5 ml) was added to a
mixture of 57 (157.4 mg, 0.212 mmol) and [PhNMe2H][B(C6H5)4] (93.6 mg, 0.212 mmol)
and the resulting mixture was homogenized by agitation. Cyclohexane (5 ml) was then
carefully layered on top. Upon standing overnight at room temperature, crystalline material
formed (including crystals suitable for X-ray analysis). The mother liquor was decanted and
the solid was washed with pentane (3 ml) and dried under vacuum yielding the title
compound (221.7 mg, 0.198 mmol, 93%) as a colorless solid. 1H NMR (400 MHz, THF-d8,
δ): 7.26 (br, 8H, o-H-PhB), 7.17 (d, 4H, JHH = 7.49 Hz, m-H-PhN), 7.11 (t, 2H, JHH = 7.36
Hz, p-H-PhN), 6.84 (t, 8H, JHH = 7.28 Hz, m-H-PhB), 6.70 (t, 4H, JHH = 7.04 Hz, p-H-PhB),
3.37 (br, 4H, CH-iPr), 2.18 (s, 6H, NCH3), 1.26 (d, 12H, JHH = 6.60 Hz, CH3-iPr), 1.21 (d,
12H, JHH = 6.60 Hz, CH3-iPr), -0.06 (s, 9H, Si(CH3)3), -0.40 (d, 2H, JHH = 3.2 Hz, YCH2).
Chapter 8
194
13C NMR (100.6 MHz, THF-d8, δ): 170.2 (s, NCN), 166.4 (q, JBC = 48.4 Hz, ipso-C PhB),
145.2 (s, ipso-C PhN), 144.3 (s, o-C PhN), 138.3 (dt, JCH = 153.7 Hz, JCH = 6.9 Hz, o-C
PhB), 126.9 (d, JCH = 152.4 Hz, m-C PhB), 126.8 (d, JCH = 159.6Hz, m-C PhN), 126.4 (d,
JCH = 153.4 Hz, p-C PhN), 123.0 (dt, JCH = 155.5 Hz, JCH = 7.9 Hz, p-C PhB), 42.1 (q, JCH
= 138.2 Hz, NCH3), 39.7 (dt, JYC = 44.5 Hz, JCH = 96.4 Hz, YCH2), 29.9 (d, JCH = 128.0 Hz,
CH-iPr), 27.0 (q, JCH = 126.3 Hz, CH3-iPr), 25.3 (q, JCH = 126.3 Hz, CH3-iPr), 5.6 (q, JCH =
117.0 Hz, Si(CH3)3). Anal. Calc for C67H95BN3O3SiY: C, 71.96; H, 8.56; N, 3.76. Found: C,
71.04; H, 8.45; N, 3.56.
Synthesis of [(L19)La(CH2SiMe3)(THF)4][B(C6H5)4] (64). THF (1 ml) was added to a
mixture of 59 (129.6 mg, 0.150 mmol) and [PhNMe2H][B(C6H5)4] (66.2 mg, 0.15 mmol)
and the resulting mixture was homogenized by agitation. Cyclohexane (3 ml) was then
carefully layered on top. Upon standing overnight at room temperature, crystalline material
formed (including crystals suitable for X-ray analysis). The mother liquor was decanted and
the solid was washed with pentane (3 ml) and dried under vacuum yielding the title
compound (154.7 mg, 0.11 mmol, 73%) as a colorless solid. 1H NMR (400 MHz, THF-d8)
δ: 7.26 (br, 8H, o-H-PhB), 7.16 (d, 4H, JHH = 7.83 Hz, m-H-PhN), 7.10 (t, 2H, JHH = 7.56
Hz, p-H-PhN), 6.84 (t, 8H, JHH = 7.28 Hz, m-H-PhB), 6.70 (t, 4H, JHH = 7.04 Hz, p-H-PhB),
3.36 (septet, 4H, JHH = 6.82 Hz, CH-iPr), 2.16 (s, 6H, NCH3), 1.25 (d, 12H, JHH = 6.72 Hz,
CH3-iPr), 1.22 (d, 12H, JHH = 6.72 Hz, CH3-iPr), 0.04 (s, 9H, Si(CH3)3), -0.18 (s, 2H,
LaCH2). 13C NMR (125.7 MHz, THF-d8) δ: 168.0 (s, NCN), 166.4 (q, JBC = 48.4 Hz,
ipso-C PhB), 145.6 (s, ipso-C PhN), 143.7 (s, o-C PhN), 138.3 (dt, JCH = 153.7 Hz, JCH =
6.9 Hz, o-C PhB), 130.7 (dd, JCH = 156.0 Hz, JCH = 8.3 Hz, p-C PhN), 126.9 (d, JCH = 152.4
Hz, m-C PhB), 126.2 (dt, JCH = 160.1 Hz, JCH = 6.1 Hz, m-C PhN), 123.0 (dt, JCH =
155.5 Hz, JCH = 7.9 Hz, p-C PhB), 65.9 (t, JCH = 99.2 Hz, LaCH2), 41.7 (q, JCH = 137.2 Hz,
NCH3), 30.1 (d, JCH = 127.3 Hz, CH-iPr), 27.1 (q, JCH = 126.1 Hz, CH3-iPr), 25.3 (q, JCH =
125.7 Hz, CH3-iPr), 5.4 (q, JCH = 117.6 Hz, Si(CH3)3). Anal. Calc for C71H103BLaN3O4Si: C,
68.75; H, 8.37; N, 3.39. Found: C, 68.70; H, 8.28; N, 3.07.
General procedure for catalytic hydrosilylation of alkenes. An NMR-tube equipped
with a Teflon Young valve was charged in a glovebox with 10 μmol of the appropriate
catalyst, PhSiH3 (0.52 mmol), olefin (0.5 mmol), and C6D6 (0.3 ml). The tube was closed
and taken out of glovebox. The disappearance of the substrates and formation of new
organosilanes can be conveniently monitored by NMR. The products were characterized by 1H (and for new compounds 13C) NMR spectrometry and GC-MS.
2-(5’-phenylsilylpentyl)-2-methyl-1,3-dithiane (66f).1H NMR (400 MHz, C6D6, δ):
7.49 (m, 2H), 7.19 (m, 3H), 4.45 (t, 2H, JHH = 3.59 Hz, SiH2), 2.47 (m, 4H), 1.84 (m, 2H),
1.58 (m, 2H), 1.54 (s, 3H), 1.47 (m, 2H), 1.37 (m, 2H), 1.24 (m, 2H), 0.81 (m, 2H). 13C{1H}
NMR (100.6 MHz, C6D6, δ): 135.5 (m-C-Ph), 132.7 (ipso-C-Ph), 129.8 (p-C-Ph), 128.3
(o-C-Ph), 49.4 (S2CCH3), 42.0 (SCH2), 33.3, 28.1, 26.5, 25.6, 25.3, 24.5, 10.3 (SiH2CH2).
GC-MS: m/z = 310 (M+).
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
195
2-(3’-Phenylsilylpropyl)-2-methyl-1,3-dithiane (66g). 1H NMR (400 MHz, C6D6, δ):
7.49 (m, 2H), 7.17 (m, 3H), 4.45 (t, 2H, JHH = 3.70 Hz, SiH2), 2.42 (m, 4H), 1.93 (m, 2H),
1.69 (m, 2H), 1.54 (m, 2H), 1.48 (s, 3H), 0.80 (m, 2H). 13C{1H} NMR (100.6 MHz, C6D6,
δ): 135.5 (m-C-Ph), 132.5 (ipso-C-Ph), 129.9 (p-C-Ph), 128.3 (o-C-Ph), 49.3 (S2CCH3),
45.1 (SCH2), 28.0, 26.5, 25.5, 20.6, 10.4 (SiH2CH2). GC-MS: m/z = 282 (M+). Retention
time: 21.6 min.
2-(2’-Phenylsilylpropyl)-2-methyl-1,3-dithiane (67g). 1H NMR (400 MHz, C6D6, δ):
4.41 (m, PhSiH2), 1.49 (s, S2CCH3), 1.15 (d, JHH = 7.35 Hz, SiH2CHCH3), other resonances
are overlapped with 9g. GC-MS: m/z = 282 (M+). Retention time: 21.3 min.
1,1-Diethoxyl-3-(phenylsilyl)butane (66h). 1H NMR (500 MHz, C6D6, δ): 7.53 (m, 2H),
7.14 (m, 3H), 4.57 (t, 1H, JHH = 5.89 Hz, (C2H5O)2CH), 4.42 (m, 2H, SiH2), 3.49 (m, 2H),
3.32 (m, 2H), 1.90 (m, 1H), 1.69 (m, 1H), 1.36 (m, 1H), 1.10 (t, 6H, JHH = 7.13 Hz, CH3),
1.06 (d, 3H, JHH = 7.15 Hz, CH3). 13C NMR (125.7 MHz, C6D6, δ): 136.0 (d, JCH = 158.6
Hz, m-C-Ph), 132.3 (s, ipso-C-Ph), 129.8 (d, JCH = 159.8 Hz, p-C-Ph), 128.2 (d, JCH = 157.8
Hz, o-C-Ph), 101.8 (d, JCH = 158.1 Hz, O2CH), 60.9 (t, JCH = 140.1 Hz, OCH2CH3), 60.5 (t,
JCH = 140.1 Hz, OCH2CH3), 37.5 (t, JCH = 125.0 Hz, O2CHCH2), 16.6 (q, JCH = 124.0 Hz,
PhSiH2CHCH3), 15.6 (q, JCH = 124.2 Hz, OCH2CH3), 12.7 (d, JCH = 112.0 Hz, PhSiH2CH).
GC-MS: m/z = 252 (M+). Retention time: 18.7 min.
1,1-Diethoxyl-4-(phenylsilyl)butane (67h). 1H NMR (500 MHz, C6D6, δ): 7.47 (m, 2H),
7.13 (m, 3H), 4.38 (t, 1H, JHH = 5.61 Hz, (C2H5O)2CH), 4.45 (t, 2H, JHH = 3.28 Hz, SiH2),
3.49 (m, 2H), 3.31 (m, 2H), 1.90 (m, 1H), 1.67 (m, 2H), 1.54 (m, 2H), 1.10 (t, 6H, JHH =
7.13 Hz, CH3), 0.79 (m, 2H, CH2SiH2). 13C NMR (125.7 MHz, C6D6, δ): 135.5 (d, JCH =
156.2 Hz, m-C-Ph), 132.6 (s, ipso-C-Ph), 129.8 (d, JCH = 159.8 Hz, p-C-Ph), 128.3 (d, JCH =
158.3 Hz, o-C-Ph), 102.6 (d, JCH = 156.7 Hz, O2CH), 60.7 (t, JCH = 140.1 Hz, OCH2CH3),
36.9 (t, JCH = 125.0 Hz, O2CHCH2), 20.8 (t, JCH = 122.1 Hz, SiH2CH2CH2), 15.6 (q, JCH =
124.2 Hz, OCH2CH3), 10.2 (t, JCH = 118.0 Hz, PhSiH2CH2). GC-MS: m/z = 252 (M+).
Retention time: 18.3 min.
General procedure for catalytic hydroamination/cyclization of aminoalkenes. Stock
solutions (1.0 mol/L in C6D6) of 2,2-dimethylpent-4-en-1-amine (S3) and
N-methylpent-4-en-1-amine (S2) were prepared. In the glovebox, an NMR tube equipped
with a Teflon (Young) valve was charged with the (pre)catalyst (10 μmol), the activator
[PhNMe2H][B(C6F5)4] (10 μmol, where appropriate), and stock solution of substrate (0.5
mL). The NMR tube was taken out and the reaction was followed by NMR spectrometry.
The products were identified by 1H NMR and GC-MS in comparison with literature data.
Structure Determinations of Compounds 57-59 and 61-63. These measurements were
performed according to the procedures described for 1 in Chapter 2. Crystallographic data
and details of the data collections and structure refinements are listed in Table 8.7 (for
57-59) and Table 8.8 (for 61-63).
Chapter 8
196
Table 8.7. Crystal Data and Collection Parameters of Complexes 57-59.
compound 57 58 59
formula C39H70N3OScSi2 C39H70N3OSi2Y C43H78LaN3O2Si2
Fw 698.13 742.08 864.19
cryst color, habit colorless, block colorless, block Yellow, block
cryst size (mm) 0.42 0.37 0.25 0.52 0.46 0.42 0.46 0.41 0.34
cryst syst Monoclinic orthorhombic triclinic
space group P21 P212121 P-1
a (Å) 17.647(2) 12.9822(8) 10.2789(4)
b (Å) 12.7738(14) 17.6370(11) 12.4964(5)
c (Å) 18.819(2) 18.8875(5) 19.0270(8)
(deg) 93.6381(5)
(deg) 90.3659(18) 90.5924(5)
(deg) 105.6381(5)
V (Å3) 4242.1(8) 4324.6(5) 2347.83(16)
Z 4 4 2
calc, g.cm-3 1.093 1.140 1.222
µ(Mo Kα), cm-1 2.61 14.34 9.96
F(000), electrons 1528 1600 916
θ range (deg) 2.46, 25.68 2.67, 26.37 2.55, 28.28
Index range (h, k, l) -21:18, ±15, ±22 ±16, -20:22, -23:22 ±13, -16:14, -24:25
Min and max transm 0.8863, 0.9369 0.4644, 0.5476 0.6226, 0.7128
no. of reflns collected 30164 34204 21301
no. of unique reflns 14225 8832 11141
no. of reflns with F0 ≥
4 σ (F0)
10473 7374 10193
wR(F2) 0.1724 0.0906 0.0750
R(F) 0.0704 0.0399 0.0310
weighting a, b 0.0890, 0 0.0468, 0.8307 0.0353, 1.9443
Goof 1.005 1.023 1.069
params refined 861 431 476
min, max resid dens -0.37, 0.66(7) -0.42, 0.62(6) -0.80, 1.34(8)
T (K) 100(1) 100(1) 100(1)
Organo Rare Earth Metal Complexes with a Sterically Demanding Guanidinate Ligand
197
Table 8.8. Crystal Data and Collection Parameters of Complexes 61-63.
compound 61 62 63
formula C45H62N3OLa C61H87N6La BC67H95N3O3SiY
Fw 799.91 1043.31 1118.31
cryst color, habit Yellow, block yellow, block colorless, block
cryst size (mm) 0.45 0.39 0.16 0.31 0.22 0.10 0.61 0.55 0.49
cryst syst monoclinic monoclinic triclinic
space group P21/c P21/c P-1
a (Å) 16.8118(15) 12.6431(12) 12.4043(12)
b (Å) 10.4226(9) 23.436(2) 13.1536(13)
c (Å) 23.529(2) 19.2756(13) 19.6160(19)
(deg) 91.8829(14)
(deg) 93.0598(12) 96.4421(13) 91.2531(14)
(deg) 95.8205(14)
V (Å3) 4116.9(6) 5675.4(9) 3181.3(5)
Z 4 4 2
calc, g.cm-3 1.291 1.221 1.167
µ(Mo Kα), cm-1 10.73 7.95 9.81
F(000), electrons 1672 2208 1200
θ range (deg) 2.84, 28.28 2.38, 26.02 2.64, 28.28
Index range (h, k, l) -22:21, ±13, -31:30 ±15, ±28, -23:22 ±16, -17:16, ±26
Min and max transm 0.6177, 0.8426 0.7717, 0.9236 0.4433, 0.6184
no. of reflns collected 35596 42441 28694
no. of reflns collected 10154 11158 15053
no. of reflns with F0 ≥ 4
σ (F0)
7748 8583 11196
wR(F2) 0.1028 0.0957 0.1065
R(F) 0.0426 0.0534 0.0435
weighting a, b 0.0495, 2.3706 0, 0 0.0535, 0.3015
Goof 1.034 1.025 1.024
params refined 461 633 698
min, max resid dens -1.50, 1.69(10) -0.42, 1.04(9) -0.30, 0.71(7)
T (K) 100(1) 100(1) 100(1)
Chapter 8
198
8.8 References
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Chapter 8
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201
Samenvatting
Zeldzame aardorganometaalcomplexen zijn moleculaire verbindingen met ten minste een zeldzame aardmetaal – koolstof binding. Kationische varianten hiervan zijn recentelijk op komen zetten als katalysatoren voor de polymerisatie van olefines en voor omzettingen van organische verbindingen.Het gebruik van faciaalgebonden stikstofgebaseerde liganden, zoals 1,4,7-triazacyclononaan, tris(pyrazolyl)methaan en tris(oxazolinyl)ethaan, hebben in het ontwikkelen hiervan een grote rol gespeeld. Echter, het stap voor stap en systematisch variëren van deze liganden is synthetisch gezien een zware opgave. Het doel van dit promotieonderzoek is het bestuderen en in kaart brengen van de reactiviteit en eigenschappen in katalyse van goedgedefinieerde neutrale en kationische zelzame aardmetaalcomplexen met liganden waarbij systematische variaties van deze ligandsystemen wel mogelijk is. Hiervoor hebben we een serie neutrale en monoanionische chelerende liganden ontwikkeld gebaseerd op 1,4,6-trimethyl-1,4-diazepan-6-amine (Me3DAPA, Figuur I). Een reeks aan goedgedefinieerde neutrale en kationische zeldzame aardmetaal alkyl en benzyl complexen met deze liganden zijn bestudeerd.
Figuur I. Liganden gebaseerd op 1,4,6-trimethyl-1,4-diazepan-6-amine (Me3DAPA)
In hoofdstuk 2 wordt het gebruik van 1,4,6-trimethyl-1,4-diazepan-6-amines als geschikte liganden voor neutrale en kationische zeldzame aardmetalen beschreven. Vervolgens wordt de synthese van een reeks aan liganden beschreven gebaseerd op dit bouwsteen (neutrale en monoanionische tridentaat liganden en neutrale, monoanionische en dianionische tetradentaat liganden, Figuur I).
In hoofdstuk 3 wordt het gebruik van 1,4,6-trimethyl-6-pyrolidin-1-yl-1,4-diazepan (L1) beschreven. Het ligand is geschikt voor het ondersteunen van goed gedefinieerde neutrale en kationische trimethylsilylmethyl en benzyl complexen van, kwa grootte, uiteenlopende
202
metaalcentra (scandium, yttrium en lanthaan). De complexen met benzyl groepen zijn stabieler dan de vergelijkbare trimethylsilylmethyl verbindingen. Dit verschil wordt mogelijk veroorzaakt door het feit dat het benzyl ligand een extra interactie aan kan gaan met het metaalcentrum. De imino groep van het neutrale ligand L2 kan gealkyleerd worden door de M-alkyl binding. Echter een dergelijke alkyleringsreactie wordt niet gezien voor met monoanionische N3O ligand L5. Neutrale en kationische complexen met ligand L1 zijn actief in de intramoleculaire hydroaminering-/ringsluitingsreactie van primaire en secundaire aminoalkenen. De substraten stellen verschillende eisen aan de katalysator: de primaire amine 2,2-difenylpent-4-en-1-amine wordt het meest effectief omgezet met katinoische (L1)Y-gebaseerde katalysatoren, terwijl de secundaire amine N-methylpent-4-en-1-amine het best omgezet wordt met meer open katalysatoren, zoals die gebaseerd op lanthaan.
In hoofdstuk 4 wordt het gebruik van monoanionische 1,4-diazepan-6-amino liganden (L3 en L4) in organoscandium en –yttrium chemie beschreven. Deze studie laat zien dat er verschillende deactivatiereacties mogelijk zijn. Allereerst kan de methyl op de amidogroep geactiveerd worden in het geval van N,1,4,6-tetramethyl-1,4-diazepan-6-amine (L3). Daarnaast kunnen ring-openingsreacties van de 1,4-diazepanring optreden. Deze worden geinititeerd door metallatie van de etyleenbrug tussen de twee stikstof atomen.
In hoofdstuk 5 wordt de synthese en karakterisatie van neutrale dibenzyl- en kationische monobenzylverbindingen van scandium, yttrium en lanthaan met monoanionische tetradentaat liganden (L6, L8 en L12) beschreven. Een vergelijkingsstudie naar het gebruik in de Z-selective lineaire dimerisatie van eindstandige acetylenen wordt beschreven in hoofdsuk 6. Het effect van ionstraal, ligand en lading is bestudeerd. De kationische verbinding (L6)-Y en de neutrale verbinding (L6)-La zijn het meest effectief in de selectieve dimerisatie en zijn zeer tolerant ten opzichte van functionele groepen. Voor practische teopassingen in de katalytische synthese van Z-enynen kan het neutrale (L6)-La systeem het best gebruikt worden, gezien het feit dat er geen gebruik gemaakt wordt van dure perfluoroarylboraat reagentia of zwak-nuclofiele polaireoplosmiddelen zoals bromobenzene. Zeer interessant is de ontdekking dat de katalysator zeer gemakkelijk in-situ gegenereerd kan worden door de reactie van ligand HL6 met La[N(SiMe3)2], een reagens dat commercieel verkrijgbaar is en teven gemakkelijk te maken uitgaande van La-trihalides en Na[N(SiMe3)2].
Gebaseerd op i) kinetische stude is naar de katalytische alkyn dimerisatie, ii) de organometaalverbindingen die tijdens en na de katalyse te zien zijn en iii) stoichiometrische reacties tussen de katalysator en het substraat is een mechanisme voorgesteld voor de selectieve dimerisatie van eindstandige acetylenen. Een belangrijk onderdeel van dit mechanisme is dat de C-C koppeling plaatsvindt aan een coördinatief verzadigd metaalcentrum. Dit verklaart mogelijk de zeer hoge selectief van deze katalysatoren. Het feit dat de verbindingen coördinatief verzadigd zijn onderdrukt het meer traditionele migratoriële insertie mechanisme, het mechanimse dat resulteerd in andere isomeren (linieair E-dimeer en vertakte gem-dimeer). Het verklaard ook waarom zeldzame
203
aardmetaalcomplexen met Cp-amido katalysatoren een hogere selectiviteit laten zien wanneer de katalyse uitgevoerd wordt in THF. In dat geval helpt het oplosmiddel het opbreken van de dinucleaire �-alkynyl verbinding. Deze laatste maakt geen deel uit van het door ons voorgestelde mechanisme en het opbreken van het dimeer zorgt voor een hogere concentratie van actieve deeltjes in oplossing.
In hoofdstuk 7 wordt de toepassing van dianionsche tetradentaat liganden gebaseerd op 1,4-diazepan-6-amine (L13, L14 en L15) besproken. De amido groep welke begonden zit aan de 1,4-diazapan is gepyrimidaliseerd en kan een interactie aangaan met Lewis zuren. In overeenstemming met ons voorgestelde mechanisme (hoofdstuk 6) katalyseren yttrium en lanthaan verbindingen met deze liganden de dimerizatie van fenylacetyleen met volledige selectiviteit voor de Z-enyn. Het (L15)-La gebaseerde systeem is de meest actieve katalysator voor deze omzetting.
In hoofdsuk 8 wordt een ander type ligand besproken: het sterisch zeer omvangrijke guanidinaat ligand [Me2NC(NAr)2]- (Ar = 2,6-iPrC6H3). Dit ligand is gebruikt in de synthese van een reeks neutrale en kationische scandium, yttrium en lanthaan alkyl verbindingen. Deze complexen en vergelijkbare amidinaat complexen zijn actief in de hydrosilylering van eindstandige alkenen en de intramoleculaire hydroaminering-/ringsluitingsreactie van aminoalkenen. Zowel het ligand als de ionstraal van het metaal heeft een grote invloed op de katalyse. In het geval van de hydrosilyleringsreactie maken de electronendonerende eigenschappen van het ligand de katalysator zeer effectief in het gebruik van heteroatoomgefunctionaliseerde substraten, het gevolg van een zwakkere interactie tussen het metaalcentrum en de heteroatomen in het substraat. Voor grotere substraten is het electronische effect minder belangrijk en in dat geval zijn de guanidinaat gebaseerde katalysatoren minder effectief dan de amidinaat katalysatoren. Daarnaast is naar voren gekomen dat grotere ionstralen de activiteit van de katalysatoren ten goede komt, hoewel de selectiviteit voor anti-Markovnikov producten in dat geval afneemt. De ligandeffecten in de intramoleculaire hydroaminering-/ringsluitingsreactie van aminoalkenen met dit type katalysatoren laat een zelfde trend zien: wanner er geen sterische factoren meespelen is de katalyse effectiever met meer electrondonerende liganden. Bij secundaire aminesubstraten spelen sterische effecte een zeer grote rol. In dat geval wordt de meest effectieve katalyse gezien bij het grootste metaal-ion.
Dit onderzoek wijst uit dat amidinaat en guanidinaat liganden veelzijdige en flexibele liganden zijn voor zeldzame aardmetaalkatalyse. Een weloverwogen aanpassing van de sterische eigenschappen van de substituenten op het stikstofatoom in de brug van het guanidinaat ligand kan ongetwijfeld gaan leiden tot interessante katalyse, bijvoorbeeld voor de hydrosilylering van sterisch gehinderde olefine substraten.
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205
Acknowledgements
First of all, I am indebted to my promoter, Prof. dr. B. Hessen for sharing his superb visions
and enormous knowledge in chemistry. I am profoundly grateful for all his trust,
encouragement, and support. Even though he was unable to be in the lab for most of the time
due to his new career, he did successfully squeeze some time to answer my phones and read
my emails; especially during the last period of my study, he stayed up very late to correct my
thesis. Bart, many thanks!
I would like to express my gratitude to the reading committee: Prof. dr. A. J. Minnaard,
Prof. dr. J. Okuda, and Prof. H. J. Heeres for reading and approving the manuscript in such a
limited time period.
I also want to thank all the people for their analytical and technical support: Auke Meetsma
for X-ray analysis (if not you, the thesis will not be this thick!), Hans van der Velde for
elemental analysis, Andries Jekel for GPC analysis, Oetze Staal for autoclave and pumps,
Pieter van der Meulen for NMR spectrometers when something goes wrong with the
machines or softwares.
My thanks also go to my former colleages that contributed to this thesis with advices and
support: Sergio, I still remember the first time I visited Groningen and I left with a pile of
references from you to get me into the field of cationic rare earth metal organometallic
chemistry; I really appreciate the advices, suggestions and help from you for my work.
Edwin, thanks for sharing the same office for a few years and more importantly for the
discussions for my work. Victor, special thanks to you for all the evening we ‘spent’ together
in the lab and advices for my research; it is you who make my stay in the lab officially not
alone.
I also would like to thank all the people that made the work in the lab very nicely during
the years I am present, in particular: Marco, Siebe, Guido, Nicky, Elena, Aurora, Kai, Itzel,
Andy, Niels, Eddy, Heloise, and Tessa. Marco, thanks for all the discussions and sharing the
same office for some time; additionally, for translating the summary of my thesis to Dutch!
My life in Groningen would not be so nice without all the Chinese friends. Although it
would be too much to name all of them, a few people deserved to be mentioned: Xiaochun
Zhang, Wenqiang Zou, Youchun Zhang, Yu Wu, Jie Liu, Qian Li, Fei Xiang… for all the
happiness and helps.
Finally, I wish to thank my dear wife for her love, support, and concern; Lili, thanks for
everything we have shared. Our little lovely daughter, Jingyi, thank you for all the happiness
you have been bringing to us! I also want to thank my parents, parents-in-law and the family
for their love and continuous support.